Thanks for all your responses, guys. I had a great conversation with my agent today and I think we're on the same page. I think the real issue was, I like my current WIP a lot more than the WOS. I think, frankly, that it's a better book...and while I'd love to just keep submitting WOS because hey, why not....the truth is I'm almost scared it will sell. Because I think I'd rather the WIP be my "debut" book. Part of this has to do with subject matter (WOS is a twist on a current trend and WIP is a lot more unique) and part to do with the fact that I just plain like the characters more in book 2.
So, agent has said she'll read the WIP and if she agrees that it's better than WOS, we'll skip round 3 for WOS, and just put all our energy into WIP. Not a question of running out of pubs or large versus small houses, really. More a question of which book I want to put forth into the world "first". ;-)
Should say, though, for the record. I still really hope to sell Book 1 someday!!!! :-D