When I first played book I on my then-new MacBook, it was pretty slow. Specifically, walking was very, very slow. When Book 2 came out, with the PC version coming first, I thought I'd try running it on my MacBook (under Windows XP via Boot Camp). The speed was actually a bit better than book I was. However, now that I've downloaded the Mac version of book 2 and am running that, it is WAY faster. A MASSIVE improvement over book 1. No slowdown at all, as far as I can tell.
It's not often that a sequel has BETTER backwards compatibility than the first game does. So I have to give Basilisk props for whatever it did to improve its graphics code. This was a very pleasant surprise -- kudos!