I used it and paralelly to the SL-C750 - and I have to say the 6000 was a very competent machine. The only thing which made me sell it off was the C1000. Once I had USB host on a clamshell model, I couldn't afford to keep both the C1000 and the 6000.
The clamshell form factor was the only reason I sold off my 6000, and even then I regret selling it off, it was such a nice machine.
Performance wise, I still think the 6000 beats any other machine out there - including the C1000 - the screen was superb, the ruggedisation, the overall fell and performance.