I have read it in the amd forums..that is best to increase the fan speed only when you are suing the GPU a lot..like playing games..or else other time you can keep it to the default one...that will increase the life of the fan....
But if its only used for gaming
then maybe you can go for more cooling in the cab...A rather orthodox way which I use is..I have got a fan more than 120mm which runs on ac power not that from your comps PSU...and keep it on the side of the cab..in a way that it throws good air on the processor and gpu section...but another thing you need to take care of is dust...so i use a vaccum cleaner to dust the cab one in 15 days...a cheap way to keep the cab cool 
But if its only used for gaming

