Yes it is. Thank you so much for your fast answer.
I found a better description of FirePro cards here http://hothardware.com/Reviews/AMD-ATI-FirePro-Roundup-V7800-V4800-V3800/?page=2
where you can read that the FirePro V7800 is over 11 inches and the V3800 is just under 7 inches. I still don't know what the exact length of the V4800 is, but it is probably fitting in the Antec Solo.