Cyclocross - fit question

I am between sizes.

the smaller size fits well with a 110/120 stem and a seat that is a little higher(6cm) than the bars. ANy smaller stem would cause my shoulders to turtle.

the larger one fits well with a 90/100 stem and the seat is almost flush with the bars..maybe 1/2 cm.

which would you suggest for a race machine?

I'm leaning toward the larger frame since I would guess the bar height would allow me a little more control over mounts/dismounts. Also the shourter stem would give me a more twitchy response for technical control rather than a road smoothness.

However I hear people say size down for cx...so I am a tad confused.

I would also hope to use the bike as a commuter.

thanks for the assist all. I do appreciate the input.

I talked with three dealers before buying mine. Two said to ride a size smaller on a 'cross bike than on a road bike -- a minimum of 1 cm smaller. The third said to ride the same size or a size smaller than my road bike. I ended up with a 'cross frame 0.3cm shorter than my road bike (smaller, but less than a full "size" smaller). The fit is absolutely fine for smooth roads, but . . . if I had it to do again, I might well go with a smaller size in order to be less stretched out. (On rough terrain, a little more upright and compact would be good.)

did the size down change your seat height much?

2 cm is my frame size difference and that causes me to have more of a drop to my bars..also makes it a little more awkward to swing my leg over.

Would a 90mm be better than a 120mm for a stem? I can pretty much size either to fit top tube-wise.

I forgot to add: the bike I am talking about is the JTS 2008.

I normally ride a 54.5 TT with a 130 stem on my road bike - I could easily go up to a 56TT with 1 100 stem...

I guess I am worried that with a 6cm drop to the bars from the seat..that it would make dismounts awkward being I would be putting a lot of down pressure on the bars.

However - if I get a bike thats too big - Im concerned I would be able to really control it (rather it would control me)

Also the shourter stem would give me a more twitchy response for technical control rather than a road smoothness.Your logic is exactly wrong.

are you saying I would be better off with the longer stem?

i think he's saying the shorter stem would give you the sort of nimbleness and handling you'd want for a technical course...