Strange, I have a gtx280 and in addition to the sensors in your screengrab, on mine it shows several VDDC sensor readings, which are all related to the mosfets, or vrms as it were. On my heavily overclocked card the VDDC temps go upto 90°C when after aone run of furmark, this is with individual copper mosfet sinks on them with a fan blowing over. In normal games they max out in the 50's. Are you sure there were no thermal pads towards the right hand end of your car when you took the stock sink off? I didn't think the 260 was that radically different to the 280.