Happy to update I swapped the chip and it worked perfectly. With a hot air solder gun the process took about 5 min. My iMac is back up and running. I would post pictures and video of the process but to your point, I don't want to encourage unethical EFI chip swaps.
The i7 870 has TDP of 95W but thats irrelevant the power consumption is of 121W and the 21.5 imac doesn't have the juice for that. But ! the i7 870S (wich is the low-power variant) has the TDP of 82W and squeezes 66.63W from the power source. Bingo ! We have a winner. I can confirm it works, i have the 21.5 mid-2010 imac with the i3 550 (dual core) now housing the quad i7 870S (2.66GHz turbo boost up to 3.6GHz, 8MB L3 cache). 4K video was a no go with i3 now plays smooth on i7, everything is blazing fast and I haven't even upgraded to SSD yet. the only thing I did notice is that in System Report I had 5.86GT/s Processor Interconnect Speed now its 4.8GT/s. Did a lap on cpu before mounting in socket, reports 41 degrees Celsius on all cores never went past 60 in full load. The i3 had 44-46 on average use and difference of 1-1.5 degrees between cores.