Yes, a Speedster would be a steel frame. Hard to know which type of steel without knowing the year and if the bike had couplers. Honestly, it doesn't really matter since all of the steel tubing that Co-Motion has used over the years has yielded great tandems. The newer ones using the air hardened steel frames are just a little bit lighter than the heat treated frames and perhaps a touch less compliant.

The Burley Tosa & Rivazza share the same ZR9000 aluminum frame; only difference would be the components noting Rivazza was the high-end model with the go-fast parts towards the end of its run. FWIW, Trek's T1000 & T2000 frames were made by the same 3rd party fabricator but had somewhat different geometry.

Cannondales seem to either be loved or loathed; only way to know is to ride one. However, given the wide range of tandems that Tandems East stocks, you should be able to ride a bunch of different tandem brands and models so long as your sizing isn't that far off the mid-point of "average". If you talk to them ahead of time they can probably tell you what they have in your size / price range that might be of interest, which could even include a Seven, Calfee, perhaps even a Bushnell depending on what they have on hand.

As noted earlier in the thread by Homeyba, it's really hard to know how a given tandem will feel until you ride one. Within brands the variation isn't all that great and tends to become simply a choice of price / weight point, where even a steel Co-Motion Speedster will feel more like an aluminium Co-Motion Robusta than a steel Santana.

• Forks play a big part even within a brand like Co-Motion where different geometry is used for their "performance" tandems with steel forks vs. their "race" tandem with shorter-rake composite forks.
• Next, wheels, tires and tire pressure comes in to play.
• At the end of the day, it's finding the right combination of frame, forks, wheels & tires that gives you the performance, comfort, prestige or whatever else trips your trigger that you're looking for. Unlike Harley-Davidson, most tandem builders do their best to make sure that you can take home a ready-to-ride tandem that doesn't need to be "tweaked" by making sure their tandems have that "right combination" at the various different price points for their different types of tandem offerings.

Again, so long as you're looking at premium quality tandems chances are it's going to be a pretty good machine. You can do all kinds of fine tuning to the ride and handling simply by making changes to tire pressure and/or different size tires to make the ride more plush or more crisp to suit your preferences. Tire size can also be used to change the steering geometry via add or removing some pnuematic trail, i.e., a larger tire adds steering trail whereas a smaller one reduces it.

I'm having a deja vu moment here because this came up once before in the not too distant past.

If selection the "Custom Frame Option" and, then yes: Co-Motion will optimize their standard frame designs to be more tailored to your team's size, weight, riding style or any another frame characteristic that you think (and Co-Motion agrees) will yield a better fitting and performing tandem.

However, if you buy a "standard" Medium size Co-Motion Speedster (for example), while you may be able to chose your color the frame's geometry and tubing will be the same as every other "standard" Medium size Co-Motion Speedster.

Co-Motion's authorized dealers "should" be able to make sure that customer who have special needs (special requirements for size, stiffness, etc) are made aware of Co-Motion's custom-frame option which, when I last checked, was about a $450 upcharge. I think in the more distant past there were slow times during the year when Co-Motion would run specials and offer the custom option at no charge, but these days I think they have gotten to a point where they are always blessed with sufficient backlog to keep everyone fully-employed without those types of incentives.