C) is the best option, as soon as the official announcments come out of ATi about the 6xxx series I expect the prices of the 5xxx series to drop, Also you will be able to see the performance and pricing points of the new cards(performance is expected to be 25%~30% better according to unofficial charts) and price is unknown. It will also of course have newer features and possibly better Xfire scaling so you may want to pick a 6750 or 6770.
So yeah... C's the best option seeing as septembers only a few days away and I expect the cards to be announced in the 1'st half of it seeing as there meant to be shipping in Oct/Nov.
4x on a pcie v2 will give enough bandwidth for a 2nd 5770. Speed maybe reduced by 2-5%, not much.
Instead of going this route I'd get a 5850 for $270 like this one - and then turn around and sell the 5770 for $100-$120 before the prices drop so the actual cost is only about the same as the cost of getting a second 5770 (mainly since his MOBO only runs the 2nd PCI-e slot at X4 which will effect the performance somewhat)
Or wait and see what comes out the next few months but remember most of the savings in waiting for the 5xxx series prices to drop will also be lost on reselling that 5770 ! (since it's value will also be affected)