I can confirm that MSI H81m-p33 with bios v1.9 is overclockable. But beware of windows updates which disable overclocking.
v1.9 bios is still available to download directly from MSI
My G3258 max OC on H81m-p33 is 4.4GHz @ 1.38-1.39 Vcore
The main thing I don't like about H81m boards is only two ram slots which are very close together and only one phase vrm for the ram.
I got my G3258 a few months ago, and its good for many older games,but there are some games which run horrible on a G3258.
Also, if any major windows process starts running in the background while you are gaming, your game becomes choppy and fps goes down.
Planetside 2 runs terrible on a G3258 since a year ago, when the game was made more multi-threaded.
I had to do a "hack" (by killing some threads) to make Planetside 2 run smooth, but the "hack" causes the animations to stop working. Here's planetside 2 on a G3258 without animations.
Skyrim runs smooth-as-butter on an overclocked G3258.
The G3258 is a "hit-and-miss" cpu. Some games run flawless. Other games run poorly. And some games are unplayable, except maybe with hacks.