A company in America has startled selling rack mounted caching systems with 500 Gig of RAM and 10 Gig Ethernet interfaces..
http://www.theregister.co.uk/2007/08...gear6_cachefx/
To give you an idea of speed, it is five time faster than the top of the range NetApp caches (NTL used NetApps, but I don't know where in the range they are).
Yours for $400,000..