Performance issues, Thermal throttling? Poor Apple Support.

Any potential solutions to my problem(s) and advice on my next step with apple care/apple genius etc. I'll try to keep this short but its been a bit of a nightmare so far.

I have owned a 15" Macbook Pro for 12 months now, which was purchased for my work in FCP and After Effects. As a windows gamer on the side I quickly came to the decision to use Bootcamp to set up a windows partition. No problem, very easy process and my games ran smooth as silk. Unfortunately about a month ago (11months after setting up bootcamp) I started to experience performance drops on both my Windows and Mac partitions, most noticably with graphic intensive tasks like gaming in Windows. Games that would stay at a steady 60fps would now drop from 60 to 35 and then briefly back up. Needless to say as a fairly experienced PC user and system builder I quickly went about trying to diagnose the problem, I tested other games and noticed the same problem which ruled out a problem with any particular game that may have been the result of a patch, I tried updating and rolling back Nvidia drivers for the 650M (and fully removing the drivers and installing fresh) I also verified that the issue wasn't restricted to Windows but certainly more prominent/obvioius. I should also point out I tried repeated SMC and PRAM resets in attempts to fix the issue as well.

I then stumbled upon forum posts of people who had had similar issues and some claimed that having the Magsafe cable plugged into their mac would cause the issue but running from the battery only would aleviate it. I was sceptical but figured I'd try it myself and sure enough it resolved the issue. I booked an appointement and went off to an Applestore

The apple Geniuses who dealt with me seemed immediately skeptical and dismissive of me and after running a brief diagnostics on my machine told me there wasn't anything wrong with it. I explained that there was no amount of problems with windows that would lead the magsafe to impact performance so badly and that after 11 months of the machine running fine on the exact same operating system and games I was convinced it was a hardware issue. They reluctantly agreed to take it in for "further diagnostics" and while it meant I'd be without my work machine for a few days I was at least pleased that I might have the issue resolved soon. Unfortunately when I recieved a call I was again informed that there were no hardware issues and that i should come and collect my laptop. The genius I spoke to instore this time was ieven more arrogant and dismissive claiming that they couldn't and wouldn't support me because I was using windows on a Mac. Again I explained that the machine had run fine for 11 months and that I had experiemneted with drivers and windows settings etc and that the only explination I could see was a hardware issue and that it seemed to me that the graphics chip was throttling due to a heat issue that was being excerbated by the magsafe charging the battery.

Met with blatant refusal to do anything to help me I jokingly asked if they'd take me anymore seriously if I took the machine back and captured the problem on video whilst plugging and unplugging the magsafe to which they responded No as this wouldn't prove it was a hardware issue. I asked to speak to the manager and after a 10 minute wait he attempted to suggest that my problem was because whilst running windows and on battery power i was using the intel integrated graphics and when the magsafe plugged in it switched to the nvidia chip. I pointed out that this made absolutely no sense as the Nvidia chip should surely see an INCREASE in performance not a drop, and pointed out that it was my understanding that Windows only utilised the Nvidia chip anyway. Not to mention that this hadn't been the case for the past 11 months. After further discussion the manager told me he would contact Apple Care on my behalf and see if they felt it could be a hardware fault. Not exactly pleased I left the store having been told I'd hear back in the next 48 hours. 4 days later and no call. I called the store back and after apologising to me the told me they'd call me back within 24 hours. Once again I have yet to hear anything.ck

So now I'm stuck with a machine that doesn't seem to be working correctly, and now performance has decreased regardless of whether the magsafe is plugged in or not. Any suggestions on potential fixes? Or who/where to contact next? (on the verge of cracking it open myself to check simple things like dust build up and thermal paste) This is all on top of the famous Image Retention issue that i've managed to more or less overlook the past year.