I only want to caution you. when I bought my first plasma I did so for the exact reasons you just posted, and I also set my budget at about a grand. I ended up with a Samsung 50inch b530 plasma and was very disappointed to find out it had terrible blacks. in fact, the dynex 32inch LCD I bought for my bedroom was quite noticeably blacker.
i'm not saying you need to spend more, they have gotten better since my purchase. i'm just saying you can't assume just because it's a plasma it will have great blacks. make sure you check that out. even at the 2k-3k range I've seen plasmas with pretty terrible blacks.
and believe me, I don't want to talk you into an lcd, don't do it! haha. but make sure you do some research, and if necessary stretch your budget to get something like the st60 or s60. it really sucks when you bring a tv home and find out it's blacks suck compared to the tv you were replacing. I've done that once, and won't make the same mistake twice. I assume nothing now. it's totally possible to make a plasma look terrible, haha
NOW FOR HELPFUL STUFF:
the motion interpolation can be turned off. it's there to try and win back lcd buyers that have become accustomed to watching terrible motion, er, 'smooth' motion
as far as gaming goes, I know that input lag has been a rather big issue with the higher end models. seems they do have a lot processing that can not be defeated. the s60 has been reported as being better in this regard than the st60. I do not know how it compares to the 5300 though.