HD 3870 sudden performance drop

[NinjaQuad9907]

Hey guys, I'm a bit new here so first of all here are my specs:
MOBO: Gigabyte GA-EP31-DS3L
CPU: Intel Core 2 Quad Q6700 (no overclock)
Graphics Card: Powercolor ATi Radeon HD 3870 (overclocked from 777 MHz to 837 MHz in core clock and 900 MHz to 1000 MHz in memory clock)
RAM: 2x2GB Kingston DDR2 KVR800
PSU: hec Rapter 500WP

So after you have seen my specs, you would probably think "damn, that's a very old build." Well, I already know that performance in any component decays overtime. I was aware it was already happening to my build, but supposedly at a slow rate. I'm not a hardcore gamer, I mostly play 3 to 5 year old games that I like, not very fond of the new ones.
In order to always know at what rate my build was losing performance at, I installed passmark performance test, one of the best benchmarking software I know now. When I first started this build, some components were different, I had a Gigabyte G31 mobo, I had a Core 2 Duo E7500 which was then replaced by an E8500 and then the Q6700. To be completely honest, I used to crazily overclock the E7500. It runs at 2.93GHz, using the stock cooler, I sometimes had it run as high as 3.29GHz without changing the cooler and it had good temps without overheating. When the E8500 came, it wasn't really overclockable since it released too much heat at stock clock. Of course, this was all FSB overclocking so I, without knowing, was putting a load on my motherboard, cuz a bit less than 2 weeks from getting the Q6700, it stopped booting with it, after a slight overclock(from 2.66GHz to 2.75GHz). I didn't leave it overclocked as while testing it it had very high temps(I use coretemp for monitoring cpu temperatures). That left me totally clueless on what to do. In the end, I had to consult a professional(2 actually). They said I had burned out my motherboard's chip, and that was why it wasn't booting. I ended up changing the motherboard to what I have now. So before I changed the motherboard and put in the E8500, I did a passmak test with the E7500 clocked at 3.29GHz. On this test, my graphics card was at least 60 points higher than the average baseline for it on passmark. Here's a link to that specific benchmark: https://www.passmark.com/baselines/V8/display.php?id=10...
I knew my CPU was holding me back, so I changed it to an E8500 first and then to a Q6700. I didn't really get to test my system much on the Q6700 right after I got it, cuz I needed some thermal paste for it first, but when I did, the performance had dropped significantly despite my cpu upgrade. It used to run games like COD World at war on highest settings @30-40 fps, PES 2013 on highest setting @60 fps, PES 2016 on highest @30-50 fps, Need for Speed Pro street on highest @30-60 fps, Need for Speed Shift on high @ 20-40 fps, Shift 2 Unleashed on med-high @20-30 fps. All that changed suddenly as it literally stopped running all those games properly, I had to run all of them on low so that they would be playable, by playable I mean anything over 20 fps and some didn't evenreach that. I had to run a passmark test again so that I would make 100% sure that my gpu was the problem. I ran one on the old motherboard before it broke down, a link to it here: https://www.passmark.com/baselines/V8/display.php?id=10...
I also ran a more recent test after I changed the motherboard: https://www.passmark.com/baselines/V9/display.php?id=11...
I really need some help/guidance on this (It would take a while to save and get another one). 
Oh and one more thing, I was looking into some graphics cards on aliexpress (sth like a GTX 550Ti or a GTX 650 or even a GTX 750 between 30 to 50 US$) Would that be a good bet? To buy from Chinese resellers? I find the price highly appealing (compared to amazon or ebay which sell cards like an eVGA GTX 550 Ti for 100 US$, excluding the shippin of course) since I live in Egypt. Tell me your thoughts on whether my graphics card is just dying of old age and my rough usage or if sth happened in the middle of all these changes I did or if there's a fix to all this.