Your results seem exactly what I'd expect, actually.
gecko wrote:But even if the laptop is contributing nothing, the i7-2600 is beating the crap out of the AMD FX 8120s.
Not that unusual. Historically AMDs can't hold a candle to Intels when we're talking number crunching. As a desktop user CPU they can scream, but even the current generation brand-new top-end bulldozer Interlagos still can't hold a candle to their equally powered Xeon brethren, even budget lines like SandyBridge-EPs... a quad of 6274s giving you a 64-core box will be about equal to a dual E5-2660 16-core box. I love AMD, but I still buy Intels. (gonna put two of these under my desk when I hit the lottery. And 32G 1066 RDIMMs are down to about $1k each! Hey, it's only money. :^) )
Also FWIW, since those FX linux boxes are just for render slaves and services, you might want to recompile your kernel with CONFIG_PREEMPT_NONE=y, CONFIG_HZ=100, CONFIG_HZ_100=y... disabling preemption and lowering the interrupt timer could eek out another ~8% for your renders, but don't do this if you want it to remain responsive under load. (or if you're a Ubuntu user, just install a "server" kernel) There might be other AMD specific system tweaks, and lux is an easy compile if you want to try any AMD optimizations...