Even though I think it would run it fine, since I have a PC setup with about the same specs, I would go for the Intel Macs.
Its a pretty big jump from Power PC to Intel Mac, just from working on video at my church. Every now and then you should be able to find a first or second generation Mac Pro. Since Apple last year now makes just dual quad core Mac Pros, you should be able to find a dual dual core somebody is upgrading from. Also eventually support for Power PC will go away as well.