"...and the linode one (at least according to ab) outperforms the slicehost."

I wonder if this is true across the board though. I imagine both providers have quite a dynamic collection of machines. New machines are being added, plans likely change over time as cash flow increases, etc. Surely not all their machines have the same performance. Some of that might just be luck of the draw. But I have never worked for a hosting provider before, so I wouldn't know.