If you need faster film, I believe portra 400 is made in sheet film. The fastest slide film availiable in 4x5 is Ektachrome E200.
Maco/Rollei were thinking about implementing a new color negative film (old agfa 800ISO) in sheetfilm too.
I'm even impressed that I know that much of the market :o Heck, I haven't tried about 95% of all films available. I Need to shoot more