I agree that getting a Vampire board is the best option. Both cheaper and faster than an A4000/040 and you get some extra features like RTG, which alone would cost hundreds more to add to any Amiga via Zorro or PCI.
If you can wait for the standalone Vampire board then you'll have a nice small, quiet and that can sit alongside the A2000 and use far less power than the A4000/040.
