Typing on iPhone, so styling is missing.
I am familiar with overheat Beverly as well, and also with good old Dells, I still using XPS Gen3 Pentium 4 HT 3.4 GHz as my main home office PC, Inspiron is for fun and games. So about overheat on XPS. I had very old IDE Dimension before, with which I had literally fried HDD (plastic actually melted) and I lost at least 40 GB of data, I was able to recover the rest. So as soon as I got XPS, I installed SMART and after one hot summer I had enough, but I did not know about PCs that much. Eventually now each HDD has cooling fan attachment, I broke front panel where the lights were and placed fan there, and as soon as I realized that my video card was not enough I got 8800 GT dual card with big fans (at that time dual cards were not as common as now). The end result - I had no fallen parts with this XPS since purchase in 2004!
Now about F1
"Regards pressing F1 on start, a Dell motherboard has BIOS that are tweaked by Dell, could that be the cause?"
I did not modified BIOS, I use right now basically original on/off power button, I am thinking about maybe trying using original USB, just to revert F1.
I changed processor still in the original case and everything was fine. The only difference is that I am using Microsoft W7 and I don't have any Dell diagnostic or support programs. This situation is embarrassing because I have Intel SSD and I cannot boot into W7 fast due to this error, ugh. But if overclock is price to pay, I will keep everything the way it is - my current CPU speed is equal to I3 from Inspiron 660 MT, so I am saving big time. Oh well, this is life I guess.