Short Answer: Go with the one that you can afford, that fits, and that handles well. Gearing, derailleurs, and stems can all be changed-out as part of the "deal".

Longer answers......

Basic info on gearing: Yes, most tandems come with wide-range gearing & XT or XTR MTB rear derailleurs (RD) these days and the gearing on the Pursuit is definitely "geared" to more aggressive teams. It's also less common to see a 52/42/30t chainring combination as 53t and 54t big rings are more prevailent (but often times excessive). That said, the gearing on the pursuit is pretty much spot-on for the 105 RD specs. Is it adequate for your needs? If you don't have a lot of steep hills and/or you & your stoker are of average size and fitness, the gearing should be adequate. However, if you are concerned about not having gearing that is low enough you would want to request that the LBS swap out the 105 RD for an XT model and change the cassette to a wider range 11x32 or 11x34 as part of the deal. The LBS may or may not try to hit you for the some additional cost for the swap-out depending on the volume of business they handle.

Additional info on gearing: Clearly, the MTB rear derailleur models have more total capacity (XT / XTR SGS models = 45t) which is suited quite well for tandems with their wide-range front chainrings and mega-range rear cassettes. However, it's worth noting that earlier models these same RDs that have been used since the mid-90s only had a total chain wrap (CW) or capacity of 43t or perhaps even a bit less which would imply that they should have come up short by several "t" on many stock tandems. Note: RD CW/capacity equals the difference in tooth count on the front chain rings & rear cassette, e.g., a tandem with 53/42/30 & an 11x34t cassette should require a RD with a total capacity of 46t [(53-30=23) + (34-11=23) = 46t] which is 3t beyond the spec. for the older XT and XTR RDs and even just a bit beyond the current model spec. So, even though the 105 is only rated with a capacity of 37t, like most derailleurs, you can usually tweak the RD B-Screw to accommodate the use of a slightly larger rear cassette (e.g., 11x32) without having any major performance issues. For tandems, it's worth noting that the full range of gearing isn't usually useable anyway, e.g., the Big-Big (53x34t) combination might be used, but Small-Small (30x11t - 14t) often times has other chainline issues such as chain drag across the front derailleur cage or chainring interference that render their use impractical.

Personal perspective: We have been using a 12-27 for 90% of the terrain we encounter for about 7 years and our regular riding here on the North side of Atlanta usually gives you about 2k vertical feet of climbing for a 25mi ride but, then again, we're a smallish (275lb) team and we climb quite well. We do throw on an 11x32 for rides where we'll encounter more serious climbs, e.g., several miles at 5% or better. Our Campy Record Long-Cage RD is only rated for use with a 29t cassette and has CW of 39t but still handles up to 45t when we have the 11x32 on with our 54/42/30 chainrings.

Value: Burley @ $1700 vs Raleigh @ $1350 vs Cdale @ $1800 vs Cdale @ $2300.

IMHO, the best value is the '04 Cdale RT at $2300, but only if your budget can accommodate it AND you would reap both the tangible and intangible benefits of a top-of-the-line road tandem. Last year's C'dale RT1000 had a big brother called the RT3000 that came with Ultegra for $3300 and rim brakes which underscores why I think the '04 RT is a great value in a top-of-the line Aluminum road tandem. As for the Burley (700c Rumba w/Tiagra or 26" Samba w/Sora?), you'd be hard-pressed to justify the price difference on equipment because that's not where it is: it's the frame that differentiates the Raleigh and the Burley. In fact, to go "apples-to-apples" on components you'd need to line up the Burley Duet @ $2449 with the Raleigh (105, Truvativ, Shimano XT hubs, etc..). So, from purely a cost standpoint, the Raleigh wins that battle as it would against the '03 C'dale RT1000 that would have originally been priced at $2400 to compete with the Burley. However, underlying all of these economic comparisons is the quality of the ride. If the Raleigh "feels" as though it handles and tracks as well as the Burley or C'dale, then your decision is easier. However, if you find that the Raleigh feels a bit loose or doesn't handle as well as one or both of the other tandems, then "value" becomes more subjective and factors into your decision.

Bike Sizing & Handling: Well, as for how the bikes will handle, bear in mind that all three tandems have different steering geometry so they will all "feel" a bit different, all other things being equal. Again, only some pretty focused test riding will yield your take on which is "best for you". I will not bias you by telling you what, in theory, the different bikes should feel like based on their frame construction or other rider's and builder's impressions. As for the sizing, Cannondale offers five different size frames, whereas Raleigh & Burley only offer 3. Cannondale's 5 sizes offer the widest range of captain's top tubes size as follows: the Med @ 21.5", the Large @ 22.1", the XL @ 23.8" (Note: There are two frames that have XL captain's compartments with different sized stoker compartments) and the Jumbo @ 24.6". The Raleigh comes in a 54, 56 and 59cm with proportionally sized captain's top tubes that I believe run close in size to the Burleys which are Small @ 22", Med @ 22.4" and Large @ 23.2". Therefore, before messing around with the stem length, be sure that the basic frame size is a good fit. Bike shops that sell tandems as a side line are sometimes very motivated to sell what they have sitting on the floor and I've seen some really bad "fits" because of this self-serving approach. Assuming the fit is otherwise good (saddle-set back position, seat height/post extension), adding 15mm of stem length to a bike isn't necessarily a bad thing depending on the height of the bars and your body size/arm length. You obviously don't want to have your upper body weight too far forward of the steering axis as that will potentially make the steering more sluggish, but I don't see 120mm being all that outrageous SO LONG as everything else is OK, e.g., saddle set-back, seat height, bar height.

For reference purposes, I use 85mm, 90mm and 95mm stems on my road tandems and personal bikes which some would say are too short. However, if my top tubes got any shorter I'd most likely have to switch to 26" wheels so the shorter stems are the lessor of two evils and, frankly, work just fine.