Here's comes some advice. I'm not going to be replying to anyone elses posts as I haven't got time to read them.
If you're hoping to end up with a 4.0ghz 6 core, there are only two routes, overclocking the FSB (technically isn't an FSB, it's an HTRef these days), or overclocking on the multiplier.
In my experience on a 790X board, overclocking on the multiplier is much easier, but with a bit more time and thought, you can reach great results on the FSB too. As you can see from Martini1991's results, with his 4.4ghz bench runs and 4.25ghz stable out of a 95w 1055t.
Either way, the loftier heights will cost you more. As far as I can tell, no Gigabyte board is capable of the 360+ FSB bus speeds needed to reach those kind of clocks on a locked multiplier. I've done a bit of reading, and the UD5 seems to top out at around 260 for most people.
If you want a board for that kind of overclocking on the FSB, it has to be the Crosshair. Lets say you go down the route of the Crosshair and a 95w 1055t. This will cost about £330. The disadvantages being it's a more difficult overclocking proceedure, but the advantages are you end up with that board, so you get the highest 890FX chipset, Trifire support, and of course, it's red.
The other route, the multi route, means you could get a much cheaper board, but you need an unlocked multiplier chip, to compare like with like, it's got to be a 6 core, and therefore the 1090t, which will cost £225 on it's own. For a board though, you can choose pretty much anything, but I'd recommend the Gigabyte 890FXA-UD5, it still has Trifire support, and the 890FX chipset, but costs £165. If you don't require Trifire support though, you could go one step lower to the 890GPA-UD3H, which has Crossfire support, the next Chipset down but costs £105. This means like for like, the multiplier option will cost you £390, or £330 if you go one step down on the board.
This is just my opinion, it doesn't take into account cooling or the case you'll be using.
These are also based on getting max clocks from the chip. Personally I'd go for the 890GPA-UD3H (how lucky, I already have one of those), and a 95w 1055t, and overclock as far as I could make it go. I wouldn't reach 4.3ghz, but I'd probably reach around 4.0ghz, and it'd cost around £265. You'd still get crossfire support, and a decent chipset, USB3, SATA3, and all the other features besides. You just miss out on the higher clocks, the option of Trifire, and the higher chipset.
http://valid.canardpc.com/show_oc.php?id=1066755 there's an old 790x that I had up over 400 on occasion. I know the current 890 gigabyte boards will boot to windows at 360+ htt and carry on up.
lol
