Couple things DaveBB-
Others are right, the performance gains you'll see from going from a 4700 to 8700(k, get the k if you go this route), will be neglibeable compared to a GPU upgrade, and your system/mother board should easily accept a new GPU. As Skuzzy said, sounds like gremlins of some kind in your settings, drivers, whatever, are causing issues. Lots of guys here able to help, post some data/intel here so people can analyze it a bit and help you out.
Regarding water cooling, there are really 2 major types of PC water cooling (there are 6 or more really, but for most gamers/PC users, 2 will do IMO), custom loops, and closed loop factory made units with the pump, fans, res, hoses, etc all in one easy to install unit. I'm sure you probably know this already. The custom setups require stand alone pumps, resovoirs, lots of fittings, hoses, and custom blocks for your GPU etc if you're doing that...much more complicated, and THESE are the setups more prone to leaking. The provide more cooling for guys looking to really push their overclocks, but IMO the factory H20 units will suffice for most of us.
I've bought 2 or 3 gaming systems every year from the same company in Calgary, Memory Express, since 1997. They have nearly 10 stores now across Western Canada, and I've talk to their PC builders frequently. They've told me one of the items that they have the fewest RMAs and returns/problems with is the factory water cooling units, from Corsair, NZXT, and so on.
I've been using the NZXT Kraken X61 on 2 systems, and an x62 on another, for over 2 years now on the first 2, and about 3 months on the x62. No problems, and others I know running the NZXT or Corsair coolers likewise have had no issues.
So, TLDR/Tildeer - don't worry about the factory units leaking, yes, there are stories online of some having leak problems, but like any PC component, there can and will be failures. Pretty slim odds on it happening to you, but if it does worry you enough to not use one, just go with a good air cooler like the Noctuas. Easy Peasy.
Good luck getting your PC upgraded, be great if you got back into the game more. I myself plan on getting into AH3 a lot more this spring myself, be good to see you in the friendly skies.