I had one Sapphire Card, the R9 280x. My experience was the same like yours so, what i did:
1. Removed/cleaned cooler
2. replaced thermal paste (the old thermal paste didnt even cover half the chip and was dry
)
With this procedure, i won 10 degrees celsius!!! from 74 down to 64. That is alot...
Maybe this will be a solution for you aswell