Cyclocross - Might be taking a dive into the CX world & have sizing questions

I've been reading on some of the posts here and on other sites that even though the bikes maybe similar the fit on a cx vs a road bike are somewhat different. I have a limited budget and was looking at a couple of sub 1k cross bikes and cannot decide if I should get the frame that's closer to my road bike or is there another criteria that I should be using.

For reference here are my measurements:
http://images42.fotki.com/v1376/photos/5/58865/249846/Duans_Fit_Calculator-vi.jpg

Here's one of the sizing chart for the Nashbar steel cx bike
http://media.nashbar.com/images/nashbar/productinfo/NB-SX1-SIZING.gif

i sat on a 2010 Focus Mares in a Medium and it felt really good so that's really throwing me off as well because their Medium has an ETT of 540

Granted each bike manufacturer is designed differently so unless i have the ability to throw my legs over all of them is there something that i should keep an eye on like a range in measurements based on my stats that I should look for?

As a matter of reference I usually ride a 52 in a Specialized road bike and 50 on my current Pinarello

http://www.cycle-smart.com/articles/secret-set-part-1-dialing-your-cyclo-cross-bike

thank you! that helps. i got a chance to swing by Performance Bike to sit on a 52 Fuji and that felt really good so i have a very good idea on what to look for in terms of geo...just have to decide which bike now

Question about sizing now. This is what i'm currently running on my road bike. A 50 pinarello. and out of shear budgetary reasons and what i've gathered from my searches the Nashbar Steel CX bike seems to be the best bang for the buck. Just trying to figure out the size to get is killing me.

As a little background i went to a local Performance Bike and sat on a Fuji Cross bike and sized up as a Small. Then i looked at the measurements and practically all the measurements are identical to the Nashbar's steel cross bike. That ETT is a 535 or a size 52 which doesnt make sense since i ride a 50 pinarello and the ETT on that is 525.

Here's the geo chart for the Pinarello (Size 50)
http://www.gitabike.com/images_cart/pi_prin_dogm_fp7_fp3_geo.jpg

Here's the Nashbar's (Size 52)
http://images116.fotki.com/v617/photos/5/58865/249846/Nashbar_SX-vi.jpg

Here's the Fuji's sizing (Size "small")
http://images51.fotki.com/v102/photos/5/58865/249846/2010fujicrosscomp-vi.jpg

Should i play it safe and get 50? or relay on the fact that i sat on a "SMALL" fuji and it has the same geo as this Nashbar

By your fit calculator results, it would seem that the TT on your road pinarello is too short, no?

ST length is a pretty meaningless number these days since every manufacter seems to measure different (unlike back in the days of horizontal top tubes when a C-C measurement could be compared between bikes). Standover clearance is way over-rated unless you plan on walking your bike rather than riding it. Important thing about seat tube height is to note that a taller seat tube can also raise your handlebar height (reduce the verticle drop from saddle to the bars). On a CX bike, you do not want as much saddle to bar drop as you might tolerate on a road bike. It is much better to have it setup for good control while you are in the drops (rather than aerodynamics) and a larger frame can help with that. With effect of handlebar height in consideration, pick the frame that has the right effective top tube length.

thanks the road pinarello being a 52.5 seems short but paired w/ a 100 stem it worked out nicely...also the pina's run bigger than the other compact frames. where i would run a 52 or so in a specialized SL3 equivalent.

But i appreciate you explanation of saddle to bar drop on a cx bike vs that of a road bike. So the 52 might actually be the right size for cross type of riding

as a side note, i've been communicating w/ nashbar and sending them my fit/measurement info and curious to see what they come back with as a suggestion