Crossfire, bandwidth and bottlenecks

[krooton]

I was planning on bunging another 7950 in to my system at some point, but some thread on here have raised some questions.

I'm running a 2500k @ 4Ghz in an Asrock Extreme4 P67 board.

Crossfire can be run at 16x/8x or 8x/8x.

I remember the difference between 16x and 8x not being much back in the PCIE2/5xxx days, but just wanted to check if that was still the case?

If that is fine, the next question would be if my cpu will bottleneck or not.

If it would, my options are to either plump for watercooling and try to squeeze more (I managed 4.3Ghz in the past on air), or upgrade.

A second hand 2700k or 3770k are the best my board can manage. Would one of them oc'd remove any bottleneck concerns?

I'd rather not switch out motherboards if possible due the hassle of having to reinstall and such.

Thanks

 

[LtMatt]

Your board will be fine, even at x16 x8. A well clocked 2700k (4.5ghz) or higher will be a good addition to two gpu's.

 

[krooton]

Cheers, done some more digging, and not much in it between the 2600k/2700k (I'm unlikely to be clocking so high that the extra multiplier headroom would matter).

Clock for clock, they are the same right?

I just don't want to cripple my 7950s

 

[swiftmetal]

If you get a decent cooler maybe an aio solution you could clock your i5 upto around 4.5GHz i doubt there will be a bottle neck or if so only on games that are relatively cpu intensive.

 

[LtMatt]

Cheers, done some more digging, and not much in it between the 2600k/2700k (I'm unlikely to be clocking so high that the extra multiplier headroom would matter).

Clock for clock, they are the same right?

I just don't want to cripple my 7950s

Same chips but 2700k is higher binned and clocked slightly (3.8ghz vs3.9ghz) higher. Both are identical apart from that. Basically you still play the chip lottery, but if you have a 2700k you have two tickets instead of one.

 

[krooton]

Cheers, done loads more digging, and it looks like a 2600k @ 4.5Ghz is doable with my mobo and cooler, and second hand prices seem to be circa £180, which isn't too much after I shift my 2500k.

 

[LtMatt]

Cheers, done loads more digging, and it looks like a 2600k @ 4.5Ghz is doable with my mobo and cooler, and second hand prices seem to be circa £180, which isn't too much after I shift my 2500k.

4.8ghz is a really good speed ive found. Aim for that or as high as you can while staying below 70c for 24/7.

 

[krooton]

4.8ghz is a really good speed ive found. Aim for that or as high as you can while staying below 70c for 24/7.

Yeah not sure how likely that will be. If my chip can manage 4.8Ghz, it would be in the region of 72ºC with my cooler fans at full pelt.

4.5Ghz is 10ºC cooler.

 

[LtMatt]

Well just go as fast as you can while staying within tolerances. Every little helps.