For May, in ORD, the break down is about 65% -200 and about 35% is -700/900. As FO's you won't for sure get a 900 checkout. I only flew a -700 trip for OE and they called it good. A month or two later I was given a 900 trip and I just told my captain that it was my first 900 flight ever. It's the same as the 700 but weighs a lot more and flares slightly different.