It is now like Dave said. I had one of the older ones with 1:66.
I don't plan on shooting heavy loads. Probably only in the 80-100 gr range. So with that in mind I will likely go with the 1:60 which Mr. Hoyt recommended.
Slowburn - as for the gain twist - that would be unique.
I've heard of some rifles having that and for the same reasons you specify.