Bike Forums - Question about size and Giant STP models

OK peeps, so I'm gonna get back into biking. I used to do some decent trials/urban assault kinda riding like riding skinny walls, wall rides, 4-5 foot drops, 2 foot+ "ups" onto ledges etc...

So I am looking to get back into it gently and it seems a lot of people recommend a Giant STP. I live in Chicago and there's a few bike shops around that have Giant STP bikes but I am confused about 2 different models and their sizes...

I am about 6 feet tall 200 lbs (trying to lose some by biking, even if its ubran assault:rolleyes: )
I want to purchase one of these:
http://bicyclewarehouse.com/itemdetails.cfm?id=9308
which seems like a more expensive and therefore better bike, as it was $900 but they are selling it for $764
It looks like it has gears in the rear and only available online as Large.

This one is available in medium and large and costs pretty much the same exact amount, but is not even on sale.

http://kozy.com/itemdetails.cfm?id=7805

1st of all, does this Reg vs Large size make much of a difference for somebody 6 feet tall wanting to urban assault (where a smaller frame is usually better, i guess) and what is up with this STP SS (cheaper) vs the more expensive but same sale price STP???? Haaalp:twitchy::mad::eek::innocent:

Ohh and that cheaper one is only 1 fixed gear in the pic, making it leet???
EDIT again... I just realized that the more expensive yellow model is actually not available in my area, any ideas on which one is better for me?