It depends which style you're making. If trying to duplicate one of the macro lagers, you wouldn't want to go any higher than about 15 IBUs. But for a Classic American Pils (CAP) more like they brewed >100 years ago, then I like about 30 IBUs in that style. I just made a CAP with 34 IBUs and thought I'd like it just a little better down a notch to closer to 30.