For the last coulpe of years I've worked on high traffic websites - we made a switch to FastCGI about 18 months ago and I have to say I think it's excellent. The big bonus with it is that we are currently running the Zeus webserver on the sites and with it's non-blocking I/O model the performance is pretty ipressive.

I'd say it's definately worth playing around with FastCGI. Apart from the fine tuning aspects the fact the the code becomes more portable (i.e. the code could run with Apache, as in your case) is a big plus point. After all what's the point in writing some nice generic modules if suddenly you have to change servers (for whatever reason) and it stops working?

Thats my 2 cents anyway.