The reviews I have seen show that the SLK800A is still the best. The 900 is next and then the Volcano 11+. I know they came out with an improved Volcano 11+ recently, but don't know how much better it is. One thing that is nice about the 11+, is the external fan speed switch. It is nice, but not necessary, especially if you get a fan for your SLK-800A/900 that has speed controls.
Dave