If you are planning to buy a mac then you are planning to target a mac audience, which means you should look at what most mac owners are using, and it isn't integrated graphics. All computers except the entry level mac mini now come with dedicated graphics cards. I would say the mac mini low end market, and possible some older imacs, are a small percentage of the whole and not really worth degrading your graphics just to support. Make your engine a bit flexible in how many bells and whistles it uses - make it scale well, that'll do better to support the low end than to OPT to buy a low-end card for yourself - yes you'd be able to test low end performance but for yourself you might as well have a system that runs pretty fast to develop on.
When I was developing on a 1GHz G4 iMac flatscreen, it was pretty decentish performance up to a point, good enough to do all the rotating zooming graphics stuff in most casual games and reasonble good creative freedom, but still limited, and that was even with a GeForce4MX graphics card. If you're going with integrated graphics you've gotta expect it's even slower than that, maybe not even half the performance. I would say that's THE lowest end, not just `low end` but rock bottom. It's just my opinion but I think you'll be much happier working on a mac with a graphics card even if it's going to cost more intially.
When I was developing on a 1GHz G4 iMac flatscreen, it was pretty decentish performance up to a point, good enough to do all the rotating zooming graphics stuff in most casual games and reasonble good creative freedom, but still limited, and that was even with a GeForce4MX graphics card. If you're going with integrated graphics you've gotta expect it's even slower than that, maybe not even half the performance. I would say that's THE lowest end, not just `low end` but rock bottom. It's just my opinion but I think you'll be much happier working on a mac with a graphics card even if it's going to cost more intially.