Hey Guys!
So made a big discovery (for me

) on installing a K2100m on a 27 2010 imac, I saw a couple people post about having issues using m2 10mm screws for k2100m and it's existing XClamp, so the XClamp thread is 2mm but the actual threading of the video card and stock imac heatsink is 2.5mm, I figured this out the hard way when my GPU basically became undone from the heatsink because the screws weren't properly latching to the heatsink and they actually pulled the Xclamp off, (along with me improperly applying thermal paste to my new i7 CPU) which gave my computer some heart attacks.
I actually used the stock X Clamp with 2.5mm 12mm screws but you could probably go as far as 14mm, I didn't get to try those out but I think somewhere between those two lengths are perfect for a 2 pipe heatsink and the existing XClamp on a k2100m. Again thank you all for everything and am excited to use my slightly enhanced imac! I have a radeon HD 1gb from my 2010 imac if anyone is interested btw!
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If you want my opinion, I had the radeon 5 series 1tb HD in a mid 2010 27 imac and upgraded to a k2100m 2gb, and have yet to notice any real gains in gaming. I'm sure it might help a bit in video editing but I was surprised, with that said most reviews say these aren't gaming cards. If you're looking to do workstation or video editing you might have better luck, but all the mxm A cards with currently functioning bioses (atleast the Nvidia from what I remember) aren't geared for gaming, I don't think many of the AMD cards are either, so consider even if you got a 4gb or 8gb beast, the chip architecture is designed for video editing/workstation/cad type stuff