Whether you get an SSD is just a matter of preference. I didn't get one because all I cared about was gaming performance, and all SSDs do is make the loading times shorter. I'd rather deal with standard loading times and spend more on hardware that gives me more frames per second. Having said that, SSDs have come down in price quite a bit since I built this computer. Even if you bought a big, expensive SSD, a budget of $2k means you'll still have ass-kicking gaming performance. The difference in loading times is very significant, by the way. It wouldn't be unusual to spend 4x as long on a loading screen with an HDD. Should also mention that SDDs are quieter, which can be an issue if noise bothers you or if your case isn't very sound proof. I can't hear my HDD, but my case is fairly quiet, so that might be why. SSDs also use less power and run quieter, if that concerns you - though both will use significantly less than your GPU and processor will.
In terms of reliability, there's debate over which is more reliable. SSDs have a more limited number of writes, but they also have no moving parts, unlike HDDs. Since desktops don't move around too much, I guess you'd expect an HDD to be more reliable, but I personally wouldn't expect there to be much of a difference.
Since you already have a couple of HDDs, what I'd do is take them apart and use them as internal hard drives for storage, and use the money that you save to get a decent sized SSD for you OS and games. Around 500GB should do the trick. You might be able to go down to 300 if you don't plan in installing many games, but 500GB would be safer. If you're willing to spend the money on it, this would be a good choice:
http://www.newegg.com/Product/Product.a ... 6820147249.
As for memory, I said that anything over
4GB was overkill. You'll still be able to play Far Cry 3, Crysis 3 and all those other demanding games on the highest settings with 4GB (assuming you don't have other programs running in the background). It's one of those things where there's no reason to go for 8GB, but since memory is so cheap, there's no reason not to do it either. It's true that games will eventually require more than 4, and even 8GB, but that's not the case right now, and it probably won't be the case for another year or two for 4GB, and you'll need a whole new PC before 8GB isn't enough.