So I definitely know that in .45 LC that +P ammo is a no no on the New model vaqueros.

Is this the same in 357 as well, or is the spicer stuff good to go?

When it comes to SAAMI pressure standards, +P ammo is essentially a different cartridge with identical dimensions, but different pressure ceilings. So, its generally frowned upon to to shoot +p in a gun that isn’t rated for it. And some +p ammo and all +p+ ammo isn’t in compliance with SAAMI standards, because its not a thing for that cartridge.

With .357 Mag, there is only one pressure ceiling per SAAMI, so as far as SAAMI is concerned, there’s no such thing as .357 +p. While much .357 is loaded less than max, anything that complies with SAAMI standards should be safe. I don’t know about boutique ammo, but any of the major companies should be fine. Among major companies, the 158gr SJHPs and SPs tend to be hotter than the more modern carry/duty ammo, if that’s what you’re going for.

With that said, full tilt ammo will beat up a gun more and might make the cylinder sloppy over time. Supposedly this is a non-issue with the GP100, but I don’t know if that’s applicable in a Vaquero. I don’t think shooting max-hot .357 would be enjoyable through one, either. That’s what Blackhawks and GP100s are for.