I think that oversize mats work best with small prints (4X5 and 5X7). The upper limit being 5X7. Broad mat borders isolate the print and draw a person in to see the small print. That is not the case with an 8X10 print because the 8X10 print is of sufficient size to be seen from a greater distance.

The mat size that I would use for all print sizes is 13X16. It utilizes full size sheets most effectively. It also allows off center vertical positioning which I appreciate.

As others have said, I think that an oversize mat on an 8X10 print is pretentious. If anything, for me, it detracts from the print.