First of all, with tons of new stuff around the corner, obviously don't buy anything right now.
I'm not saying any of this is confirmed, but by following recent possible "controlled" leaks, new macbook pros may include upwards of an Ivy Bridge 2.7Ghz quad core and iMacs upwards of an Ivy 3.4Ghz i7 quad. Both also having the possible update of "retina" displays which will double the current screen resolution.
Another developing option is the external thunderbolt->pcie enclosures from Magma and Sonnet which will offer 1-3 pcie slots over thunderbolt to allow macbooks and imacs the ability to interact with card-based systems (PTHD, SSL Madixtreme, pcie SSD storage, etc.)
If you want lots of dedicated internal storage, huge amounts of RAM, or true server xeon processor chips, then you'd be looking at a Mac Pro, but (even being the owner of one) I think we're slowing passing the time when the Pro is necessarily the "best" vs. "best for certain applications."
Now in regards to the firewire question, from recent speculation, apple might remove direct firewire ports on the computers (assuming those who need it will adapt over thunderbolt). I haven't experienced any issues myself using firewire drives on a pre-thunderbolt macbook pro and mac pro, both on PT9 and PT10. That's only my experience and YMMV, but here's to positive thinking