I have the Solo as well, and I just put in the same factory OC'ed EVGA 8800GTS 512. Actually, I bought the Solo a year ago, and never put anything in it. At the time, I was considering getting the 8800GTX when it first came out. But when I read about the length of the card, I went and measured the case. Results? It was very close. The problem was that the manufacturers were giving different specs for their cards. In the end, someone found out that the 8800GTX needed slightly extra room than what the drive cages were offering. Given that the 9800GTX is as long, if not longer (since one would need to worry about the orientation of the power plug now as well) than the 8800GX, it would not fit into the Solo without some major fixups.
Anyways, sorry you had to find this out after you got it. Cheers on the 8800GTS 512!