Need two FireWire ports - what are my options?

I'm in the market for an iMac. Currently, I use an external hard drive, connected via FireWire 800, as my Time Machine drive, as well as some external storage. I also have another interface hooked up via FireWire 400. It's very important that I have both of these drives plugged in at the same time, but the new iMacs only come with one FireWire port (my MBP has two - one FW800 and one FW400).

I really want the power of the new iMacs, but not having two FW ports is absolutely a deal-breaker - I simply can't work without both. I know that one option is to go with a Mac Pro, and I am considering this option but the biggest thing holding me back, of course, is the price. I suppose a FW hub is another option, but I don't like that idea as it'll decrease the performance of both devices hooked up to it.