is the width of the factory rear tire pretty much the widest?

i like the look of a wider rear tire, but know almost nothing about tires other than that car tires = dark side of the force...

i still have the factory one, but think another couple of inches would be awesome.

You can go a little wider but be prepared to mod the fender.
at 150 check the bolt heads on the inside of the fender for interference.
and change to carriage head or truss head bolts.
and forget about saddlebag brackets.