I would think a SSD would be better at handling VM. The macbook air with SSD has been out for a while and there aren't many reports about them going bad and VM is always on with OSX. Two times ram for VM on a different Duo vs. an Air would be very different, 36x2=72mb or 2gbx2=4096mb. Swapping 4096gb would be worse than 72mb I think.

On a different point. I was thinking of doing something similar recently and found SSD drives and DOMs (they're more similar than different) from Kingspec all over Ebay. Might be a cheaper route and they're also IDE.

Either way, if you pull this off I would really like to hear the difference in performance.