I've had a couple of pairs of left handed kevGloves for quite some time now, and have found that taking them to the east worked out pretty well. I'm a west-coast skier, who enjoys them thoroughly. And, I found no marked decrease in performance when travelling back east and skiing them at killington and wildcat. Or even nashoba valley!
BUT when they really seemed to shine is when I took them skiing even further to the west. My home is in california. Travelling from a location of approximately 119.81 degrees west longitude(Reno, NV) to 172.51 degrees East longitude (Mt Hutt, New Zealand) caused the gloves to become even warmer! In fact, when I unpacked them from my suitcase upon arriving in New Zeland, there was steam coming out of them!
Apparently, taking the gloves another 67.19 degrees of longitude westward increased the thermal properties of the gloves. This is despite having used them skiing at places so inhospitable that the icy winds have been known to blow cars clear out of the parking lot and sent rolling down the mountain. So therefore Bec, you may be onto something here.
I'd hate to have to use them in Europe or someplace like that.
And, good luck in your search for the perfect hand warmers.