Have never had problems with either of min falling over under heavy load, I can't gaurantee that you won't however.
I'm a fairly heavy user, but I wouldn't say that I ever put too much stress on either of the routers (mainly because I spend so much time with my speed limited having reached the end of my allowance early in the month - you VM guys think you have it bad.....) but they do get a fair hammering.
The one upstairs (the WRT54G) is several years old now and, as I said, running custom firmware - it's still as solid as the day that I bought it
