Unless there is a need to push the chip further, the gains are very small
I had a Phenom II 955 stock was 3.2 GHZ, any over clock passed 3.7GHZ gave almost nothing back in performace or benchmarks.
If you download AMD Overdrive it will tell you how much thermal headroom you have to overclock further (I assume 40 c temp is under full load?)
System - Runs Cool and 100% Stable
AMD FX 8350 @ 4/4.2GHZ, Corsair H60, ASUS Sabertooth 990FX R 2.0, 8GB AMD R9 2400 MHZ RAM, 3GB AMD R9 280 GPU, Crucial 240GB M500 SSD, Seagate 1TB SSHD. housed in a Corsair Carbide 300R Case with Corsair CXM 750W 80+ PSU