I can't comment on the speeds, but are you sure you need a laptop? What you get in portability, you trade off in hard drive capacity, unless you really want to pay for it.
Just to put things into prospective, the cheapest MBP goes for $1999, which gets you a 120GB HD and 15" screen. The iMac price equalivant gets you a 250GB HD and a 24" screen...same processor, same amount of RAM.
If you're looking at a 17" MBP, you're looking at $2700-2800. If you drop $2800 on an iMac, it gets you the same processor and RAM as the 17" MBP...but a 750GB HD (and 24" monitor).
I mention this because it sounds to me like the 200GB may not even be enough for you. I'd make sure you need the portability of a laptop, and probably read up on external drives. I have a 160GB Lacie USB drive, and to me it's absolutely cavernous. But a lot of these external drives aren't the fastest thing in the world. It does well with individual files and there's no noticable lag. But when opening up folders with tons of data in there, it does lag a bit. I'm talking folders that are over 2GB or so, there's a definite wait compared to my internal drive.
Hope that helps,
-Nick