I hope external Thunderbolt SSD's will keep much of the same performance characteristics as the internal SATA ones, but there's no way to know that until there

I hope external Thunderbolt SSD's will keep much of the same performance characteristics as the internal SATA ones, but there's no way to know that until there actually are some thunderbolt devices :). Having a good performing external SSD would be pretty sweet, as it could be a painless and relatively cheap way of upgrading your iMac. It comes down to how much overhead you get if you go over Thunderbolt, and how good the Thunderbolt -> SATA chips will be.