I've read that the max temp on the 350C V1 model is equal to the V2's 250C.
Does the V3 with 260C allow 10C higher temperatures than either? or did they simply adjust the temperature sensor slightly so they're all the same temp?
Yep, read the sticky on the Extreme, it covers most of that. There's also a big thread on the Extreme which covers that and more. You can ask your Extreme related questions there.