Anything more than 12-13 psi without an IC isn't a waste, yes, it is going to be hot, but, if it didn't still make power than it wouldn't be common place amongst OBS PSD and first gen cummins guys, let alone most of the pulling trucks. Yes, intercooling will help drop intake and exhaust temps and probably make more power, but, even with heated air, it is still adding cylinder pressure.
Yes, the turbo is probably outside of it's efficency range, but a Non I/C Cummins H1C is well outside it's efficency range pushing 40 psi on a 5.9. Yes, a bigger turbo will make cooler air and probably more power, but it will still work.