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#11
ian! the processor will fit without any problems, the only difference between ATX and mATX is the fact that the mATX has less expansion slots, ergo, the size of it.
BTW, if you're adding a PCIe Video Card (the HD 5670 that you have in your system specs) you don't need the 880G Chipset, you know? the difference between the 880G and the 870 Chipset is that the 880G has on-board video (HD 4250) and the 870 Chipset doesn't, of course the 870 is a little less expensive and since you don't need the onboard video, you could save up a couple of pounds :)
Here's what i've found in Novatech!
Asus M4A87TD/USB3 AMD 870 (Socket AM3) ATX DDR3 Motherboard
Gigabyte GA-870A-UD3 AMD 870A (Socket AM3) ATX DDR3 Motherboard
MSI 870A-G54 AMD 870 (Socket AM3) Motherboard
The Gigabyte 870 is a little more expensive than the MSI 880G but Gigabyte products are top notch!
Of course these are ATX boards, if you need a mATX board, then i guess these aren't the best choice, but still, the same thing again, ATX boards have more expansion slots which opens your possibilities for adding a better sound card, a PCI expansion USB card, well, there's too many options to choose.
Bottom line :) you'll go fine with either Chipset and either board type (ATX, mATX) the processor will fit and it'll have no problems whatsoever. So, choose one, buy and enjoy
Cheers.
EDIT:
870 Chipset: No on-board video, 1 PCIe 2.0 @ x16, if the board has 2 PCIe, the 2nd slot will work at x4.
880G Chipset: HD 4250 on-board graphics, 1, 2 or 3 PCIe 2.0 @ x16, the boards with 2 PCIe works at x16 and x4, the ones with 3 PCIe works at x16 (single), x8/x8 (dual) and the other PCIe works at x4.
890GX Chipset: Same as 880G but with a different on-board video card (HD 4290)
890FX Chipset: No on-board video, from 2 to 5 PCIe slots, configurations from x16/x16 (dual), triple x16 and x16/x16/x8/x8 in a Quad Crossfire configuration.
Hopefully i didn't confuse you too much