Cervélo P3 sizing advice

Hello

I'm in the verge of ordering a Cervélo P3. I will be doing it online, so no chance to try it before (no Cervélo dealers around).

I'm 1,92cm (6'3") and trying to decide between sizes 58 and 61.

I have recently done a bike fit with my bike, but the frame is an aero road frame (that I use in road and TT positions) so I can't exactly relate the measurements to the Cervélo. But any way here is an image while fitting.

http://imgur.com/a/SCs7B

Seat post is at 81,5cm, stem length 100mm, 175mm crank arm

And here is the bike geometry, size XL



And the Cervélo geometry



Looking at the stack I would have no doubt going to the 61, as it's almost the same stack I have now. But I feel 61 could be a little too long and I'm afraid to be too stretched.

On the other hand, maybe the 58 is too low for me.

Bike fitter leans more towards 61, but I don't want to miss.

Any thoughts?

Thanks