It turns out that #4 cable is rated to go to 150A up to 100'. The smallest cable size for a 200A application is #2.

There is probably a "fudge factor" involved but if you don't plan on using more than 150A very often it should be fine.

Another option is to use the #4 as a 10' to 15' stinger if weight is a factor.

http://store.weldingdepot.com/pdf/weldingcable.pdf