One thing to mention. Those temps will not cause slow down in gaming, and it will have nothing to do with it. Something else will be causing that.
As for Intel temps, 51 degrees is high but should be fine, and for a presscot which I think it is, it's pretty normal. Though I guess its stock?
If it was an AMD processor, you'd fine it'd be reletivly easy to buy a cheap one, fit it up, and it'd be much cooler (maybe even 20 degrees cooler than a standard).
With a Pentium though, this job can be a harder task since you might find some fan/heatsink combos turn out hotter than the standard heatsink...so you have to be more careful with the disicion, so just look around. I would give you a good one, but the mag with reviews of them are at home... I'll post later on with some
As for water cooling, it can be an expensive option, but if your willing to go for it then yeah. This would dramatically decrease temps though it can be hard to set up def, and if you don't have a big enough case, or knowledge of piping, it can get more so.
Once you get past that, and you tighten connections as much as possible just as a precaution of leaks then it'd be way worth the effort
Hope this helps