So I'm planning on lifting my loyale 2 inches and I was thinking of going with a 15 inch rim and 25 inch tires. I'm gonna redrill my hubs for a six lug and go with six lug rims, but I want to do as minimal cutting/bashing as possible. What sort of backspacing on those rims should I be looking for? 

There is a list on here of most 6 bolt rims that are useable on subies. It lists all their dimensions. Older Toyota rims are the standard go to because they have a similar backspacing. I believe it is 4.5 or 5". I'm not sure how the math goes with change of backspacing and its effects on clearance but you should be fine. No one seems to have that info and you will most likely be told to scour the bigger tire and rim thread in the Offroading forum to see what people have done. I believe you can run a 25" tire with no lift. People run 27" tires with a 2" lift and sometimes don't have to trim anything or they have to trim a bit. The variance on that would be from offset, sagging suspension, real tire dimensions and I'm sure a few other things.

I've ran 25 inch tires with no lift, though a pair of the wider ones did rub just a little bit.  if you don't plan on lifting then stay under 25 inch actual diameter.  at 25 inches or a bit over you will likely rub.  you have to look up the tires, the normal tire ratings are generalized and not exact.  same deal for 27's and the lift.  I wouldn't try to eek out that last centimeter, be conservative.

 

the reason the backspacing is important is to center the weight of the wheels over the bearings.  with our small light cars its not ultra critical, but bad offset can eat up wheel bearings quickly depending on the situation.  that said I have seen tons of people running with spacers, and odd offsets with no issues that I have heard.