I spent an hour at our local reclamation yards looking at reclaimed oak beams and struts, as well as green oak (green = freshly felled) and air-dried beams.
I decided to go for an 8-month old semi-air-dried section which is pretty straight for 2.8m and then kinks off at about 5 degrees for the last 0.7m. I only need 2.5m for my staircase strut, so I plan to use the end nearest the camera, which has a nice long shake (split) in it and is interesting to look at.
I decided against using a reclaimed timber just because this is a major structural strut and most of the beams I've seen have been fairly well insect-ridden or split over the years. Plus, greener oak is a darn site easier to cut and chisel!