Probably part of it it's because I was running it from a usb-pen live, probably it's because I only have 1g of ram and a weak 945 video card.
To be honest, I'm not sure that running off a flash drive should be any slower, as long as it's a decent USB 2.0 drive plugged directly into an appropriate port on the laptop (i.e. not via a slow hub which has forced it back to USB 1.0 speeds). A good flash drive can't manage the same sustained transfer rates as an internal hard disk, but the seek times are much
better, and I would have expected that to be the dominant factor in performance in a situation like this where the game needs to load small amounts of data frequently.
Also, my mac mini had 1GB RAM when I first started playing Book I
(though I've since done a home upgrade to 2GB), and it's got an Intel GMA950 on-board adapter. However, I suspect the biggest differentiating factors are either the amount of time Apple have spent optimising their graphics drivers (the joys of a closed platform), or potentially the CPU, depending how much of the rendering your drivers are managing to offload to the graphics hardware.
Despite the fact that they are different platforms, however, I'm still rather surprised your experience seems to have been quite so different to mine.
I'm no informatics expert but I think the intel graphic drivers for Linux suck. Badly. They're open source and all that but this is more of an excuse for Intel to not care and let others do the job.
I am afraid it is so, because onestly an nvidia 6100, which is integrated in my old pc's motherboard, can't be MUCH better than this card I have here. That card is very old and has no dedicated memory but what the hell it runs on linux games that I can't even starting to think of running here ! With an old amd processor, one of the first 64 bit as I remember correctly, and no more than 1 giga of ram.
Or maybe it's the game that it's not optimized for Linux, but that is the programmings language fault I guess.