I wear white PI sunsleeves. Everyone is going to have different comfort levels, but I haven't found them uncomfortable, at speed, even on hot (for MN), humid days. If you're moving slowly and there's not much evaporative cooling, yeah, bare arms feel better, but then you're dealing with smearing sunscreen and having bugs stick in your arm hairs. And yes, they're effective - I'm not a glove wearer and the backs of my hands are darker than my arms in the summer, even with sunscreen on them.
Also, I don't wear the sleeves for early morning/evening rides - if I'm not going to be in high-angle sunshine, I'm not wearing them.