Why should I prioritize top tube length over stand over height on a CX bike? I purchased a 50cm CX style bike from an online retailer.  After assembling the bike and filling the tires, I found only had around 1&quot; of stand over in bike shorts.  Since I will be commuting on the bike and using it for transportation around town, my preference would be for something with greater clearance over the top tube for the following reasons:

Saftey - being able to dismount quickly in an emergency situation
Clothing choice - I won't be wearing bike shorts when commuting or riding around town
Cyclocross - I do plan on riding the bike off-road, so more clearance would be better on uneven ground.

Now to my question: I emailed the retailer asking for assistance selecting a smaller size, but they &quot;strongly recommend&quot; sticking with the 50cm frame stating it would be &quot;perfect&quot; and that the top tube length is more important than stand over height.
What is the thinking behind this advice?
UPDATE
I kept the bike and am overall pretty happy with the fit. I've used it for commuting, long distance rides and a few races.  It's also survived a collision with a bus and lived to tell the tale.  Luckily, I wasn't seriously hurt.  I can also attest that the stand over height didn't make a difference in that scenario.
Why should you prioritize top tube length over stand over?
Because top tube length affects fit and stand over does not affect fit.
When you are riding the bike stand over does not affect fit.   

My CX only has 1" of stand over.
A big triangle is good for stiffness and shoulder carry.
A tall top tube means faster transition to shoulder carry.  

I don't get your reasons  


1" versus 4" should not affect your ability to dismount quickly.
You ride on the seat - not the top tube.
In a controlled dismount the bike is stopped - 1" is a quick and safe stand over dismount.
If you have to bail because a truck pulled in front of you then lay the bike down - don't stand up.
So your clothes touch the tube?  What is the harm?
How is more clearance better on uneven ground?
When you stop then don't stop over a hole.
If you fall on the top tube an extra inch of clearance is not going to save you as your feet are not going to be under and you are going to be moving.
Even with 2" of clearance falling on the top tube should always be your last choice.