No, it's not worth it when for $25 you could get a Xeon x5460 modded to fit your socket 775. It adds 4MB cache and has a higher multiplier of 9.5 so you can reach 3.5GHz at just FSB369 with less stress on the motherboard, and because it's a 45nm chip will draw only ~105w at that speed which is exactly what your 65nm B3 stepping Q6600 uses at the stock 2.4GHz. At 3.0GHz the 45nm Quads draw just 72w while your B3 Q6600 there is 125w. So if your reason for changing is temperature, go 45nm.
The Gigabyte Ga-965p-ds3 is
verified to work with it and it's not surprising your BSEL padmod didn't work because Gigabyte boards use a lookup table instead of reading the pads. You will need a
BIOS modded with added microcodes. And preferably a 2.0 or 3.3 rev board, as while the 1.0 board uses the same BIOS, it only has a three-phase power VRM.
The even better x5470 with a multiplier of 10 is probably too expensive to be worth it at $50, double the price. But even that is the same price as a Q9650 with its multiplier of 9, which doesn't need any modded BIOS.