Well I suppose in a standard game I wouldn't let wish grant a +6 bonus, just because I do like to maintain the pre-epic bonus ceiling. So yeah, an epic spell would be required.
(In my own games I use Lesser Wish, which can grant inherent bonuses at a rate of +1 per 4 levels, so I'd let Lesser Wish grant a +6 bonus. I feel that restricting inherent bonuses to the high-high levels is silly, but that's neither here nor there.)