First of all, Intel motherboards are actually cheaper than AMD. If you want higher end features, then it becomes rather even. Around the £100 price is when AMD motherboards introduce more extras over Intel.
A i5 could most likely run the same amount of bots as a FX 8150 anyway. Why? Glad you asked.
A Bulldozer has low IPC (instructions per clock) and a Intel i5 has far more. Therefore as you multitask a i5 can do far more calculations quickly and reduce the overall load on the CPU whereas the Bulldozer has plenty of cores to spread the workload on even though it has dreadfully low IPC. You could probably squeeze one or two more on a FX 8150 than a i5 3570K.
The FX 8150 is not even 8 cores. It's 4 real cores and 4 module cores. If it was 8 cores the heat and power usage would go through the roof. It's a bit like Intels Hyperthreading on i3 and i7 models. You can find graphs about this all over the internet. Games are not optomised for this so it once again reduces the amount of strain you can put on a Bulldozer.
Sadly, I find it hard to explain so if you want a better explanation of it all it's best to look at some websites about it