Lots of questions here.
1-> Is it worth it?Only you can answer that. Do you want to push them harder or are you too afraid of screwing up something? Personally I'd push them. More bang for the buck.
1a-> You don't exactly need them for a very small overclock but nobody ever does a small overclock do they? Get the Hyper 212. Even if you end up buying another CPU it fits lots of sockets.
1b->Once again not exactly needed. The case while being an important part of your system is also kind of not important. Cable management can be done with time and patience even on a small case and a drill can get you some more fans in place if needed.
2+2a->You could get a new GPU but it may be bottlenecked. But like you said you can keep it for when you upgrade the system.
Last question-> If you have money to get a i5 2500k system then by all means do it. But before that try overclocking and tweaking around with your current system. You will get a kick out of it and get some experience for when you do get that 2500k
Yes, lots of questions! Thank you so much for your generous answers! I will take your advice to heart and continue tinkering.
I'm learning a lot already. For example, the problem can't have JUST been my PSU being dirty (which is what I *thought* was solved): When I put the side panel back on the case (with 120mm exhaust fan on HIGH) the system crashed within a minute or two.
So, I'm back to thinking that I should order a case fan and the Hyper 212 and see where that gets me.
One more question: can you really get that much accomplished with cable management?
Well the case will limit the airflow no matter how good your cable management is but bad cable management can seriously reduce the cooling inside the case.A difference of 5Cº or so can be meaningful.
Anyway case fans are cheap so it wouldn't hurt to get another one
UPDATE: Went ahead and installed the intake case fan (only place I could on the Sonata III case, behind the HD cage). I also replaced the rear exhaust Antec Tri-Cool with the other Cooler Master fan.
Seems to be running cooler now, especially the CPU (went from 55c max to 51-53c in Core Temp). GPU on FurMark (1680x1050, no AA) topped out at 80c, both before and after the intake fan was installed. The difference seemed to be it got to 80c slower with the intake fan.
STRANGENESS: What I also found surprising was that using the Tri-Cool on the HD cage to test out the various RPMs (1200, 1600, 2000) seemed to show that higher speeds didn't actually cool anything more! In fact, 2000RPM caused the GPU's heat on FurMark to climb rather than dip! No idea why that might be.
NEXT STEPS: This weekend I'll test out the Hyper 212 Evo on the CPU. I'm wondering how it will do if the GPU is still heating up and not getting direct cooling from a side intake fan or vent.
QUESTION: Would a PSU with a good 120 or 140mm exhaust fan pulling air from inside the case and not just from the PSU itself help with any of this?
While I hear what you're saying about the case not being so important, I'm starting to think I just bought too hot of a GPU for this case. Radeon 4850s were hot from the start, then I went and bought a factory-overclocked model to put in a case with poor airflow. Genius.
If money is not a problem then you could get a better case. You could also get an side intake fan. Some cases are already prepared for this others require some...ahem...destruction of property. Nothing a small drill can't handle