You don't mention why you are considering surgery, but I really hope it is not just based on the measurements. The numbers you mention (30-40) are really not in the surgical range for an adult, unless you are having other issues such as pain that has been refractory to all other treatments. If you are very athletic now, I do not think you will enjoy your new, fused spine unless you are doing surgery strictly to relieve pain. If you are not having significant pain I would strongly recommend deferring surgery at this point, for as long as possible. I am curious why two surgeons recommended surgery for curves of 40 degrees or less, as it is really outside the standard of care.
Gayle, age 47
Boston brace as a teen for AIS
Oct 2010 fusion T8-sacrum w/ pelvic fixation, TLIF at L4/5.
Feb 2012 major A/P revision for broken rods
mom of Leah, 12 y/o, diagnosed Jan '08 with 26* thoracic JIS (age 6)
4/08 26 degrees, brace 16 hrs/day
9/08 17 deg. OOB - brace discontinued
9/09 30 deg, resuming brace
5/10 VBS Dr Luhmann Shriners St Louis
5/14 stable 4 yrs post-op, 14* T
also mom of Torrey, 9 y/o son, 12* T, decreasing spontaneously (from 19*)