That's great you got 275Mhz. Mine is running 200Mhz reliably. The included fans keep the heatsink temps under 100 f. I also have a small external fan to keep them cool. Higher freq is nice, but 200 Mhz was what I was expecting to run them at as a minimum. I find the latest build of cgminer buggy and takes up a lot of CPU for some reason, so I've resorted to using last year's version.