You would lose much more with enchanting, but at level 87 you can get about 90k an hour, if you concentrate. To find out how much you would lose, find your xp to 99, then find the xp of enchanting (d stone) to 87, then multiple that xp by .75. Divide the xp to 99 by that, then multiple that by the price of cosmic runes. Do the same with 87-99, except use the xp of onyx enchant.