I thought that 285's have a chance of fouling on the suspension? And that 295's is where it fouls 100%.
This would explain why many BA XR owners run 275's.
I'm sure if you flared the guards, strengthed some components and stuck some 2.5cm (huge) spacers and longer wheel studs you could probably squeeze some 315's under the back end without a chance of fouling, 325's would probably be ok as long as you don't power around a corner, as then you are guaranteed to rub..... But i would think the cost of strengthening the back end to cope with the extra forces applied by running spacers wouldn't be worth it, if you are working to a budget.
Bigger cams and an edit would probably be cheaper.......
But I could be wrong, as its all second hand information.