My instinct is that they would be much different, and likely much cooler than bare arms, in an arid climate. Like, when you first put them on it's like there's a strong fan blowing on your arms, they're so much cooler than ambient. Once they're saturated, which happens to me in 10 minutes or so, the cooling effect is at equilibrium, so it's the same as bare arms.
But, I've never even seen the PI sleeves. The fabric of the DeSoto sleeves is very different from the Zoot, so I wouldn't be surprised if other brands are also very different.
The other thing is that any cooling garment must be skin tight. If it's not, it'll just trap heat, like those goofy gel bandanas.
Speed comes from what you put behind you. - Judi Ketteler