In reply to Robin Woodward:
Ive just spent part of the morning conducting static load tests for T rated axes. One of which is the 'buried axe' test or at least the test that most closely simulates that scenario. The difference between the 'pass' figures here is 3.5KN for T vs 2.5KN for B. The way the test is carried out is the load is applied centrally between 2 points along the shaft 500mm apart. In real life the snow would offer a more even support along the length and much reduce the bending moment. The loads are just the pass figure, most axes will support more than this anyway.
In short.. I wouldn't worry about it. I think by the time you take into consideration the dynamic top-rope that a buried axe belay would suggest plus the dynamic nature of the snow you'd be hard pressed to reach those loads anyway. In a rescue you'd have to be hauling 250kg to get close to the rating of a 'B' axe.
Where the T test makes a big difference is in torquing picks and stein pulls found in more technical climbing.
I'd get the axe that is most suited to the climbing in general.