speed issues

[spartaneye]

hi,
I'm running virtualbox on a intel macpro dual-core 2x2.66ghz tower with 4gb of ram. I've installed freedos on a virtual machine and am trying to play some of my favorite freeware games from when i was a kid. I know DOSBox is a perfectly fine way, and very fast emulator for this purpose, but I'd really like to get the virtual machine running well just for fun. I'm running into issues getting decent performance out of the machine. Running old games like the first several commander keens, and crystal caves, they run between 1/2 speed and 2/3 speed. I'm shocked that I can't get better performance out of this, which makes me wonder if I've missed some setting that needs to be adjusted to better utilize my system. If anyone has any idea how to fix this, I'd appreciate the info! Thanks!
- Doug