Yeah, it's C, GPU-Z gives C by default.
Actually, for an 8800GT 40-50 is fine, that's not a bad idle number of many modern cards. I have five case fans, an open front, pinned cables for airflow and recently vacuumed (which totally did save 5-9 degrees) and the lowest I can get the card is down to about 40 in a 20-21 room. I could jack the case fans to high, and the card fan to max but I doubt I get huge savings from it, since my case sides are already cold to the touch.
My case for reference since ZanShadow mentioned Antec, although it is an older model, it's 98% the same except they moved the drive fan to a better location and minor tweaks. (The old location actually is fine for airflow, as my hard drives are really cold from it, but it's hard to route the SATA cords by. They'd probably be frigid with the new location.) Plus I got it when they had a bad fan batch but couldn't tell which batch it was, so they just packed extra fans in with every case. And mine were all fine so I got bonus fans, and of course used them. (And it's the best case like ever and I will use it until they change standards enough.) (One more note, I leave the door open because I'm paranoid and also like access to my optical drives, but closing the door has only ever seemed to add a degree or two after an extended period that I could tell when I tried it. I'm sure they added vents to it for a good reason though, mine is flat like the rest of the door.)
Not to take away the temp issues JaoSming's got, but I do come back to that side-fan and back-fan. Even though they're large and people were really hardcore pushing that design for a while (it was a religion!), I had a case in that design and the thing always ran hot no matter what. The only way to get decent temps was to disconnect the side fan, pull off the side of the case and blow a floor fan in which made the back fan useless but at least actually flowed air through. The motherboard of that computer burned up and became useless within three years especially because neither the north nor southbridge had a fan on them except the one in the side of the case. Which again is shitty airflow. It's basically a fan blowing on one part of the board and another fan hoping to suck out hot air. Whereas the other method pulls in a bunch of cool air (even in 90F heat) and the back fan/fans drag it through and out. (And if properly placed, like in that Antec case, across the hottest areas. The moving of the power supply is just a bonus.) Even with that shitty design and my old 6600GT idling in the high 50s it's still a good card if I ever need it, real problem on the 8800GT's is that design flaw they have. Early Wii's have the same issue, overheating kills them a lot faster than it should.
I have no idea how that side-fan, back-fan crap started, where's Paul23 to figure out a way to stop corporations from being stupid about case design.
Just for comparison, I have a 77F room right now, and the 8800GT I have is "ilding" in C (with Google Chrome) at 46/38 with the PCB at only 32. Fan is only 35% too.