Hi,
There are number of posts related to frame sizes, but I hope I could still get some help in the particular case.

I am 164cm with around 75cm inseem (without shoes). The standover height on my current mtb bike is on the level of 80cm. When standing over without shoes, I feel some presure on my crotch, but with the shoes on, it is acceptable (I can lift the front wheel by almost 10cm).

I have decided to purchase second bike to be used for road riding and some off-road as well, therefore was looking for a cyclocross one. After some search, I have decided to go for Specialized Tricross Pro frame (as mentioned in another thread) and purchased 49cm one based on the simple correlation to my inseem (0.67*75=50.25cm).

Looking more into the geometry table I started to think, whether I took the right decision, or should go for one size bigger? Comparing both sizes I found the following:
- Wheelbase difference is on the level of 1mm, so clearly neglectible
- Seat tube angle is decreasing by 1 degree, while head tube angle is increasing by .75 degree
- Seat tube lenght is bigger by 3.5cm
- The standover height is increasing from 75cm to 77.3cm
- The effective lenght of TT is increasing from 515mm to 530mm
- Head tube lenght is increasing from 110mm to 125mm

So inspite of the small angle difference (I am not sure whether it can be called small) the bigger size is basically a bit higher (2.3cm) and longer (1.5cm). Both frames are much smaller to my current MTB (with the effective TT on the level of 580mm).

From the standover height perspective both sizes (even 54cm) are ok as they are smaller than my mtb.

1. Did I choose the correct size (50.25cm is just a bit closer to 49 than to 52)?
2. Will I feel the size difference when ridding both sizes?
3. I assume, that by playing with the steam lenght I can get similar ridding position - is that correct?
3. What would be the general impact of the bigger size in case of ridding position - more upright?
4. Road bikers tend to choose smaller sizes compared to their body geometry - is this to get more laying position?

The bike will be used for some long distance ridding and touring. I plan to participate in some road marathons, but for sure I will not ride as typical road racer, e.g. with very aerodynamic position (I would hit my belly with my knees for some time).

Was my choice of the size correct, or I should change for bigger size? The frame is just 10 miles from the shop, but soon will be over a 1000, so change will not be that easy.

Regards,
Adam