If you are not overclocking the phenom would be the better option. If overclocking there will be some games that will favor the 6100 but only some because it can reach a higher speed, but then again not woth $30.
For the record, AMD says that a single Bulldozer module has around 80 per cent of the performance of two conventional CPU cores. In other words, a four-module Bulldozer core should be at least as quick as a six-core processor.
That being said, the 6100 is a 3-module, 6-core cpu. 6*80% = 4.8 true cpu performance. The issue is in light threaded applications, you still take the 20% hit, so the phenom II comes out slightly ahead.
So the real question is will the game you plan on playing use 6 cores or only 4. Most games only use 4 cores, but the newer games are becoming core friendly (BF3, Civ V, Dirt 3, ect)
IMO, $30 isn't worth the difference for a few games, go with the cheaper Phenom II. If they were the same price, flip a coin.
could anyone break down the technical differences between the 2 besides the obvious core amount? would be appreciated
The main difference is the actual architecture of the CPU. The "bulldozer" CPU cores are arranged into "modules" each module contains 2 integer processing units and a shared floating point processor. So what AMD may call a 6X in the FX-6100 is actually a 3 Module with 6 integer processing units and only 3 floating point processors. Compared to a TRUE multi core design such as the Phenom II 965 has 4 cores, 4 integer processing units and 4 floating point processors. The FX CPU's have a quite garbage IPC (how much work the CPU actually does per cycle) Because of this a Phenom II 965 @ stock will out perform an FX@ 4.0 Ghz core for core. OC the FX to 5Ghz and the Phenom II to 4GHz and the IPC still holds true. I suggest the 965