See here:

   https://en.bitcoin.it/wiki/Scalability 

It's based on the posts I made to the micropayments thread, updated with the newer, more accurate ECDSA speed figures from Hal and m0mchils suggestion of optimizing the protocol by only broadcasting block headers and merkle trees when a solved block is found.

Please do improve it.

Good job on some worthwhile calcs.

I'm not clear on this bit here,

where is the incentive for somebody to fund building of such rig? Is it the transaction fees that will accrue or will this sit on the front end of mining rig?