Some thoughts, others may disagree...
My ambient temp is also around 23c~24C all the time. I've grown accustom to my CPU idle temps, with an i7 920, 930, and i7 3930k being around 31c~33c. My motherboard temps around 32c. That could be do to my cooling solutions, case design, etc. What's important is the fact the 38c is not out of line, and you shouldn't be concerned about it.
If you're interested in checking your frame rate in all games, just download FRAPS...
FRAPS show fps, record video game movies, screen capture software
You'll see the FPS in the upper left corner of your screen, (or whatever corner you designate), such as the screen shot I've posted below.
Your GTX 670 is a very good card, but you can't expect that it won't slow down during periods of maximum pixel pumping. If you find there are games in which you want to increase the performance, you have two options...
1) You can reduce the eye candy, or the resolution in the "settings" menu.
2) You can add another GTX 670 for SLI operation, and that will slice through anything....well, for about 18 months, anyway.