The limiting factor you have to deal with is the 2.75 rim width. A 140/80 is as big as you can go without the beads being pulled in too far in relation to the section width. Even then, a 140 on a 2.75 inch rim gets pulled into an oval, egg-shaped cross section. I always found the handling on road (and off road grip) better with the stock 130. In fact off road, I'd go for a 120 every time.

The 140s (various brands including TKCs) that I tried all tended to wear quicker in the centre because of the change in cross section and there was less mechanical grip because the contact patch is reduced, despite it being a wider tyre. A 150, although it will just about fit between the swingarm, will amplify this problem further (unless you lace a wider rim to the standard hub). Wider is not always better.

Have a read of this thread I started a while back about TKC (TwinDuro) tyre size and speed rating permutaions. It relates to the XTZ, but the principle is the same.

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