Never heard of "Whistler", but just finding this (below) in Google, would make me consider it and give it a go, especially if that is all your supplier is carrying now. I guess the big question is "how well will it grow here" vs the old standbys?
"Whistler Winter Peas are a semi-leafless, SWEETER WHITE flowered pea with yellow cotyledons. They are winter hardy down to 0 degrees F. Whistler winter peas are white flowered, with a very low anthocyanin content (the reddish, purple color on flowers, leaves, and stems). Studies have shown that the lower the anthocyanin content, the higher the palatability of forage. Austrian winter peas are purple flowered, and have a high anthocyanin content. Sweeter feed means higher intake, higher weight gain, and more profits"http://hancockseed.com/whistler-winter-peas-50-lb-bag-848.html