CoolerMaster is good, definitely not the cheap crap you find in bargain-basement PCs. It's a name that has been around for a while.
If you can get a high air flow for your intake fan it could help to add vented slot covers for the expansion slot covers between the cards (or just remove the slot covers) this can help remove some of the hot air from around your cards.
Silverstone vented slot covers:
I agree with the adding fans in the side panel blowing into the card intakes.
Also pay attention to cable clutter within your case.. try to eliminate or reroute cables which may block airflow.
Higher grade power supplies usually have modular cables which can be removed if not needed helping improving airflow in addition to the power savings from the higher efficiency.
Thanks for the fantastic reply. This was exactly what I was hoping. I'm temporarily running caseless until I get my new 120mm Scythe Kaze Jyuni. Anyone know if this fan is any good? http://www.ebay.co.uk/itm/330601649625