That spread in rate is not all that huge; that is a total spread of 8 lbs, which is +/-1% from the mid range value. I would not call that dismal; I'd call it normal manufacturing tolerance.
Hi, I agree with what you say and there is certainly a lot of science in it. As an instrument fitter myself, I am familiar with tolerances (and you are right that the fancy digital readout does not change the accuracy, but does fool many people!) But don't forget that I also checked a set of Trick Flow springs and all (except one) were within 2-4 pounds of spec. Which is pretty well right on. The one that wasn't was a new replacement spring I bought last month, same part number but totally different batch number (as in approx 12 years apart). And the older ones were run in but only around 1 year use. So I would say that that gives a good baseline for accuracy and the Comp springs were all over the place in terms of variations. As they are new and after run-in I would expect the values to drop a little and since they are all under in the first place, I would still consider that to be on the dismal side.
Unfortunately I won't have access to the Rimac when I assemble the 340 heads so won't be able to shim them too accurately. I do have my own home made valve spring tester but it is only good for springs upto about 300 pound