2nd/3rd week of May... going to be getting into "runoff" on a lot of western rivers... so I would think "tailwaters" if that's the direction you go in.
If it were "me", that time of year, and one crazy trip to burn... I would head to Roscoe, NY... immerse yourself in the "fertile crescent" of American fly-fishing. All those fabled Catskill rivers and great hatches (I think everyone should fish at least
one good Hendrickson hatch in their life). That's probably a little out of your range... but it would be epic!