[strat61caster]

I'd be happy with any of the main three, Eibach, Hyperco, Swift.

Swift is relatively new, I was using Eibach and Hyperco 10 years ago. Arguing between the three is pretty silly, if you care you'll compare all three on the relevant specs and the choice will become obvious they are all accurate enough unless you are prepared to invest in measuring each spring you get yourself (been there, done that). I've got Eibach on my car now and a pair of Hyperco's on the way, Swift doesn't make the spring I need right now but I'll probably try them in the future.

That thread from NAM is very old, and his data isn't very precise but it proves what low end springs give up for a price point and what you get spending the extra money. You can set up your own spring tester with a bathroom scale, some weights, spring clamps, calipers, and a bit of diligence and understanding that you're ghetto setup is going to have inconsistent data, but it would be enough to prove that your two 7k springs are actually 7k and not 6.5k and 7.3k, if you've got a press of some sort (drill press, hydraulic press, a shock dyno will do the trick as well as a big ol' vice) and a high capacity scale or load sensor all the better.