I just bought a Phenom II x4 830 to replace a 840 last week. I OC'd the 840 to 3.9 GHz @ 1.488 Volts, while I OC'd the 830 to 3.5 GHz @ 1.367 Volts. Despite the 400 MHz disadvantage the 830 beats the 840 in every gaming benchmark I could throw at it.
In the 3DMARK 11 test alone I saw an astonishing 1000 point improvement!!!
I then submited a Stalker Call of Pripyat benchmark score that received a better then 91% of all other submitions ranking, up from a 82%... that's a 9% increase in ranking, and the only difference, is the processor, and the voltage setting.
My Windows 7 WEI processor score dropped from 7.5 to 7.4, however my memory score somehow went up from 7.5 to 7.7, perhaps having a L3 cache takes some of the burdon off my system memory.
My Super Pi scores are now slightly lower as well, for what ever that's worth...
In real life gaming I've noticed a huge difference, Borderlands 10 FPS improvement, and in BFBC2 I now rarely drop below the 100 FPS mark, and thats on ultra settings!
The cherry on the sundae is, my temps max out about 12 deg. lower on the 830, I have yet to see it get hotter then 39 deg., my 840 would hit 52 deg. while stress testing.
Phenom II x4 830 vs Phenom II x4 840... Come on... it's a no brainer the 830 by a knock-out!

Cheers
Edited by Diamondhead - 11/7/11 at 11:42am