In Oblivion, my stealth PC uses potions-poisons on her arrows with great results. The best is a 5 effect potion made from Harrada, Spiddal Stick, Frost Salts, and Milk Thistle. Damage Health 8 points for 30 seconds, Damage Magic 15/61, Silence 26 sec, Frost Damage 9/38 and Paralyze 3 sec. At Master level, two of those will take down about anything. If shot at long range, the timed effect of one shot will kill 'whatever' before they can get to you (most of the time). The 3 second Paralyze is just long enough to get off a second shot if they are close. Three of the ingredients are found inside the Oblivion Gates and the Milk Thistle is found just north of Dragon Claw Rock. Or just tour around to the various venders and buy them. Would not go inside an Oblivion Gate without 30 of them.