An SXi Pro is just as fast as an sxr, both in stock form. I had 2 sxi pros and an sxr at one point in my family and my sxi pro was actually a bit faster than the sxr in chop.
They get a bit better fuel economy but not that much better, they do ride less on the nose and feel lighter and more nimble. They carve great and you can rail turns and also enjoy great jumping. I enjoyed my sxi pro very much, never had any issues with they way it handled or rode AT ALL. The SXR does have more bottom end.
Either way you can't go wrong in my opinion. I would choose an sxr just because they are newer, and they do carve much better, but both ski's are great.