Win7 64 bit Pro only takes about 20gb. A 64g is good for OS and a few programs. A 128g is a popular choice.256g tend to have better read/write times. As of now, anything larger has insane pricing.
As far as 200gb of games, a 10000rpm velociraptor would do good for less $.
The main plus for SSD's with games is the initial load time. After that, no noticeable difference.
this one had 356MB/s reads (the only thing im concerned with) which is better than all sata2 drives, the PCIe ones looked really good with 600MB/s reads but i have to keep my pci slots open for tri-fire and quad fire (lol)