A collapse on embark can cause a lot of problems...some of which are spoilerific. Suffice it to say that a collapse on embark can cause significant lag...one reason is that magma or water may start flowing and possibly never stop, and the flow calculations are expensive.
If you're getting consistent collapse-on-embark wherever you embark, I've heard that can happen if world gen messes up and you get a corrupted world. It's said to be fairly rare, and to not have anything to do with your world gen parameters or seed, so that if you extract the world gen parameters and re-import them, you should be able to gen the non-corrupted version of the same world without weird collapse-on-embark bugs. Corrupted worlds sometimes have massive skylines (like 1,000 z-levels of sky, instead of the small number they're supposed to have), massive spikes of adamantine, magma in strange places...yours doesn't sound weird enough that I'm sure that's the problem, but it's a possibility.
Of course, there could still be some site-specific collapse-on-embark bugs going around, like the ones that Toady was working on fixing not long before release, but if you try a bunch of different locations and consistently get a collapse, it's time to gen a new world.
Re-downloading the game might also be a good idea, in case the corrupted world gen could be due to a corrupted download of df, but it also happens with fully correct copies of df sometimes, from what I've heard.