I ferment lagers warm (for a lager that is, actually ale temperatures) under pressure, now my SOP. At higher than normal temperatures it results in a superior lager character. I tried an ale under pressure. Even at normal ale temperatures it resulted in a very un-ale-like character. Much more lager-like, but also underattenuated, which is never a problem with lager it seems. If you can find it on his website, Scott Janish tried IPAs under pressure and found them very bland. I wouldn't recommend it for ales. Like RPh_Guy said you can just ferment your ale warmer without the pressure and probably get a more satisfying result.