Thats excellent result. I've got friends who use autocad-3dmax combination and they say that there r options to speed up rendering process in 3dmax but u have to be 3dmax expert for that.
I rendered this weekend one picture with archicad internal lighworks, using photorealistic sun (thats slow drastically but add very fine shadows), on intel dual core 2.0 with n-vidia 7600 graphic card, 3300x2500 resolution. Rendering time: about unbelievable frustrating long 12 hours.
Did u use some speeding up tricks in 3dmax or just putted skylight and some sun and reduced quality (number of rays etc.)?