[dmitril]

If one is looking for something exact cutting is the only realistic way. I cut my springs, many others do too and so far there is only speculation as to what might go wrong from guys who suggest against it. If you can provide an example of an actual problem you encountered then sure, until then it is bad advice to tell someone to spend extra money on springs they don't need.
Cut 4 loops first and check how much fps decreased. Next cut should be the same or less, the more you have cut off the more fps change removing an extra loop will result in.

Edit: I've been proven wrong, stuff can go wrong, I cannot imagine the mode of failure that leads to warped spring guide with a 150 fps cut spring when 500 fps unflattened cuts dont warp a thing for me, but it can happen.
Edit2: Mode of failure is likely not enough force from the spring to guide piston onto spring guide, I'm guessing this happened with an aeg.