There USED to be a post with the various links required for each sprocket combo. I can't seem to find it anymore, although I'm sure it's out there somewhere.
Another option you might consider is running a dual-sprocket in the rear. Someone on here has done that... he just uses 2 different chains and picks the one for the type of riding he is going to do.
BTW, I'm using 15/55 combination and I had to cut 3 or 4 links off of a 130 link chain.
Check this out: This is a good read
Also: TW 200 sprocket calculator