How do I check fan speed on my Macbook Air?

Darkeyes has some good suggestions. Not sure you need SMC fan control because your fans appear to be working - i.e. ramping up to deal with the heat. Most people use SMC to make the fans ramp up when they won't. Also You already have Istat Pro so you can monitor the CPU temp and fans speed from there.

Next time you notice the slow down and the fans maxed out like that go to activity monitor. Finder/Applications/Utilities/Activity Monitor. (or there is a little tab on the left side of Istat Pro that will bring up Activity Monitor. Important! Make sure you have "All Processes" checked in the pull down menu in the upper right panel. Then hit the %(percentage) tab at the top and if there is a process that is using a lot of CPU it will show up there at the top. Take note of what it is. If it's a Kernel panic don't do anything, but it could be something that you can safely "Quit" - Quit Process is the red stop sign in the upper left corner. I was on my sister's white Mac Book the other day and noticed it was really hot and the fans were maxed out. I went to AM and found that there was an old Canon printer print job spooled still running using up 100% of the CPU. I Quit it and everything went back to normal (fans slowed, temp went down) - So you might us AM to monitor this next time it happens to see what's up.

Good luck.

M.

Download SMCfan for mac (google it) which can not only show you your fanspeed, but can also regulate it so you can fix it up to a constant value if you want. Also it shows the temperature of your CPU.

6200PRM is max for the Macbook Air. But it's normal for a Macbook Air as the thing gets hot overtime.

The problem you are facing is called a 'Kernal panic'.. Monitor you CPU performance when the slowdown occurs, you CPUs will be in Full Throttle (Do this by using ACTIVITY MONITOR... Just type it in finder). This panic mainly occurs since your Macbook Air's temperature has reached Critical point (mine does this whenever the temperature exceeds 90 Degree).

A quick solution to this is to just put the thing to SLEEP and wake it 5 seconds later and everything will return to normal. However, I would advice keeping the Back end of the Air raised by a Laptop stand as the panic is due to heat not ventilating out cause you keep it on a soft surface and the vents get covered by it as the Air's weight pushes it down in the soft surface.

I used to have a lot of problems, but recently, I started following the above steps and the thing hasn't stalled for a long time.

Have you upgraded to SL 10.6.4 yet? I used to have heat problems on my MBP before 10.6.2 came along and fixed my problem. Not sure that's is but it's worth a try.

Good luck

M.