In reply to Ramblin dave:
Ok, the OP was asking about straight shafts, not alpenstocks. I have a 60cm Mountain Technology straight shafted T rated axe. I use it regularly on terrain up to grade II, for belays, cutting steps, etc etc... Two tools get in the way on easy rocky stuff, and one is best for arresting in easy angled snow gullies. Its my tool of choice on that sort of terrain.
I played around with a cirque of similar length and it was pretty good, but I preferred the weight of the MT axe for cutting steps, as I'm working towards my winter ML.
I would say to the OP don't get too hung up on a dead straight shaft, there are loads of good T rated alpine axes on the market, the bottom of the shaft is generally straight enough to be good for plunging but if you must have a straight one you will find that a second hand MT one is likely to be bombproof. If you want something good for plunging, more important than the profile of the lower part of the shaft is the shape of the ferrule/spike- if serrated or hollow it can be hard to plunge in to some sorts of snow. Current advice is not too long, ie if you want a walking stick get trekking poles.