4 out of 5 gpu's working !!!
I first tried vmalloc=256MB alone which caused the nvidia kernel module not to load. Adding the uppermem line fixed it and 4 gpu's started. I added another 128MB (which should have been ample) but still only 4. I know gpu 5 is good. It seems there must be some other problem.
grub now looks like this
title Fedora (2.6.21-1.3228.fc7)
kernel /boot/vmlinuz-2.6.21-1.3228.fc7 ro root=/dev/md5 video=vesa
ff vga=normal vmalloc=384MB
I have posted the bug report