Have you flipped the overclock switch? Im not entirely sure, but if you havent, I think the card will throttle to stay within 375W, potentially rendering your overclock pointless.
yes i have flipped the overclock switch.
before i did my Mh/s jumed around a lot.
now its steady.
also waranty is void once you put a waterblock on the card.
but it runs a lot cooler. never goes above 50Deg C
Is it cheaper to cool them with water than air con or other methods people are using?
50c is very low - is it costing more to keep them that low?
well there is the intial cost of the waterblock, pump radiator and fan.
your looking at $120 for water block, $70 for pump, $80 for rad(120x4), and $20-$40 for fans. (depens on what fans you get. I use Scythe Ultra Kaze 120MM fans)(best bang fro buck i think)
you need about 1 fan per GPU, so with the above configuration you could cool 2 6990's (my 50Deg C is colling 1 6990 and 1 5770 video card) ambient temp around 27 deg.
other disadvantage is that any maintance you want to do it could involve draining your loop, and refilling. and if your not careful, posible leaks.
advantages are where you put your rads. I cut a hole in my cold air duct and am not venting the heat into it which heats my house. (sub zero temperatures and i havn't turned on the furnace yet)
I also have 4 6970's watercooled on a single rad(4x120) and GPUs doesn't go above 53 deg. (45-53 deg)
in the summer i plan to just put the rads outside in a box and dump all the heat out there.
I guess your need to factor in your air conditioning costs. how much it takes long term.
then there is setup time. and if you enjoy this. I have been watercooling now for 8 years, and enjoy it as a hobby.
once its set up it just runs.