I use conventional oil too. Used it in my Celica every 6000ish miles 'till I sold it a couple years ago with....
264,000 miles on it!!! And, the compression was still within spec!!! The car ran great, but figured it was time to move on (was tired of not having A/C). And get this - I used SuperTech from Wal-Mart. It gets good reviews on oil analysis. But, I recently noticed the price jumped from $7ish a bottle to $10 WTF??? That puts it in the same price range as Valvoline, Quaker State, Mobile 1 and other 'brand names' (though, I'm sure SuperTech is a 'brand name' re-labeled). So, I'm going to re-research these oils and see how the Used Oil Analysis (UOA on bobistheoilguy.com) comes out on them.