I got all the answers to your questions... first of all, there will be no performance decrese since you only use one OS at a time. There will be though, as someone stated, decreasing performance the longer you got Windows installed, and the more things you install in it. (This will not happen on a linux system.) The OS is preferably installed on your primary drive since your bootblock resides on that one. It can be changed though, but I can't see why anyone would do that. (especially with Win, since it's a pain to change...)