Air Transat has tight seat pitch.
But considering it's $455 cheaper, I would go for it (and I have made similar analyses myself in the past and flown Air Transat). The worst thing that can happen is that your flight is delayed for a few hours, but that happens on the majors too. So far I've had nothing but good luck on Air Transat (although the breakfasts are quite pathetic, the dinners aren't too bad).

I doubt the miles gained would have a cash value anywhere near $455, unless you are near a threshold.

[This message has been edited by WillTravel (edited Mar 17, 2004).]