I have recently fitted a gt28rs with the larger exhaust housing I find it very laggy but brutal when it comes on boost. I was thinking of fitting the smaller 0.64 housing what are the pros and cons of both these housings?

they are a laggy turbo, the smaller the housing the smaller the wheel you need making less hp but faster spool,
If its spool your after go for a hybrid are you running 16vt or 20vt

Yes the .64 housing on the GT2860RS is better suited to a 2L.

This is exactly why I've always used a 0.64AR turbine housing on all my turbos, starting with a GT28RS, then onto a GT2871 and now a GT3071

Yes, I know I'm sacrificing peak power, but I'm always going to see positive boost before 3,000rpm and full boost well before 4,000rpm

Running a 20vt I've got the smaller 64 housing I'll fit it the weekend and see what happens