I'm seeing somewhere between 8 and 15 minutes per generation on a single-processor Barton 2500+. It is, indeed, much slower than the last protein (but mind you, it's still quite a bit faster than the one before it ).
No, your numbers don't seem all that far off, in other words... especially considering that you can't use both CPUs for one protein (you need two client installs for a dual machine). Because when that's part of the picture, your setup and mine are fairly close (2400+ vs. 2500+), assuming your MPs are Barton-core.
Edit: Scratch that, it's anywhere between 5 minutes and 20...