Maybe get a 560 if you can. Will perform better than a 550 Ti.
That PSU is overkill since you arent going to SLI, 500-600W is the recommended for the 550/560/6870.
Get a cheaper H77 mobo if you arent OCing, it will save you some $ for a better GPU.
Windows 7 Professional/Home Premium would do okay.
Except for that cooler - I really hate to recommend plastic water blocks when strong air fans will give you the exact same OC results. The OCZ Vertex isn't a good choice either as they're known to have issues and errors.