I'm not sure what the difference is between those models. The former 8200 vs 9000, the 9000 had a inner-cooler for the turbo and the 8200 didn't.
I used a 8540 a few months ago and I was surprised at the difference between it and my M9000. It felt like I had 15 or 20 more HP and there shouldn't be but 7.
You could gain up 10% more hp by changing your engine oil and trans fluid.