The FX 8150 (not FX 8100, unless it is another one of those canceled chips ie; FX-4110) also had a 125W TDP. The FX-8350 would be a good upgrade from your I5-2500k, if you were using it for more than gaming. I.E; C++ compiling, video editing or just heavy multi tasking in general like running a game in windowed mode while browsing the web and writing code or map editing. Generally the i5-2500K and FX-8350 have the same gaming performance, therefore it would not be an upgrade in that sense.
Personally if you were going to throw a chip in there, already having a i5-2500k, I would go for the $130 FX-6300, it would be good to have for a multi-tasking/coding computer and AMD makes Overclocking a lot more fun than just bumping up the Vcore and multi.