for bolt actions best and strongest arent always in the same category. A 150 should be more than enough for the rifle, anything more and it will be a pain in the a** to pull the bolt back. However, if you do end up wanting a higher spring let me know, I have a 210 Ill sell you.
Check out this site,
http://www.airsoftsniperforum.com/Plenty of great info and helpful people on it.