So rather than look into water cooling for the pair which from what I gather is going to cost an absoloute bomb due to the amount I'm going to have to pay for VRAM heatsinks and so on, I'd like to get a card or 2 cards which are better than my current pair.
I will be looking to watercool them/it, but I'd like a model with a standard PCB rather than non-standard as it's nigh on impossible to find a waterblock which can fit.
As for price, I'll be selling both my current cards on eBay or to anyone else who has an offer they'd like to give for the pair and with the money raised, I'll be using that to put towards a new card.
If anyone would like to make a suggestion as to what could be worth getting, then please let me know.
Will also be open to offers for my current cards which are both in great condition, have had no overclocking done and have all original packaging and other contents.
A single 580 would be pretty good if you can get 150-200 for each card. A step below and you could look to buy a single 6970 or a 570. Each of these would probably won't sound like you have a formula car inside your house.
None of those single GPU setups will be as fast as your dual Gigabyte GTX 470 SOC's. I'm a little surprised that you are having noise problems, as those fans are supposed to be practically silent. To improve the noise, you should look at your case ventilation, clean things out, separate the cards for more airflow, etc.
The only upgrade that would make any improvement in performance would be a pair of GTX 570's or 580's. The Gigabyte GTX 470 SOC is significantly factory overclocked and generally runs as fast as a stock GTX 480/GTX 570.