There's quite a lot to say here but it basically depends on your upgrade cycle - there is no right or wrong.
An i7 with ht off is an i5. They will clock the same and perform the same.
With ht on the i7 will oc slightly lower for the same volts because the ht increases the power demand. This decreases performance per core but increases overall performance across the 8 threads.
This doesn't mean that an i5 is going to bottleneck in the near future but a 2600k is still more future proofed. This is because the point at which an i5 would bottleneck would be the same time that you could turn on ht on the 2600k and keep using the chip because games are increasingly making use of more threads.
Technically this could be taken to the next level with a 2011 - cherry pick the best 4 cores to OC on in the meantime and switch back on the others and then ht when you need to in.the future. However the cost of getting this setup is £800 which is 1.5 times that of an i7 build and twice that of an i5 build so to get the value out of it you need need the chips to last proportionally longer since we aren't making use if the extra threads any other way. Currently the 2011 socket also has the advantage of not being end of the line which IB is to 1155. The intel socket plan i saw recently had x-e continuing past IB-e so you would have the option of only needing to upgrade the mobo or cpu rather than both.
So back to the upgrade cycle for gaming:
If you are the kind of person who will get around to upgrading the cpu every year then the i5 is for you since you'll never use the spare capacity of the other chips.
If you plan on keeping the cpu for a couple of years then the i7 quad core could come in useful, especially if you run cf/sli since you have to feed more gpus. Aria currently have a great deal on a 2600k for just £210 which admittedly I'm very tempted by!
There are several people on this forum who also swear by the x-e range and have bought them for gaming. They keep their mobo/cpus for 3+ years and get their monies worth that way plus have the versertility and power in the short/medium term. You have to keep the hardware alive for a longer time this way too though...
@ NotSoBright,
All are good options, none of them are bad chips. Just pick the one which suits your needs.
