Thanks for the vote of confidence. The weight was actually at least 60 lbs, but I compensated by removing the weight from elsewhere in the car to maintain my normal race weight. Nonetheless, after having raced it for years while sorting out the jetting and keeping records as detailed as possible, the car was at least .05 faster and possibly up to .10 after a 1-2 # leaner jet change.
True, it wasn't a totally controlled back-to-back test because I don't have the time, money or resources to eliminate all variables. But the results from my test based on good record keeping showed a benefit on my particular combination. If I wasn't sure of it, I wouldn't have went through the trouble of finding weight elsewhere to remove and put up with the extra difficulty of pulling the trans or center section because the exhaust system is in the way. With the restrictive rules we have in Stock, even small gains can be difficult and expensive to find. So I take them where I can within the rules and my budget.
A similar situation exists with other exhaust "tricks". Merge collectors and step headers, - they have helped some cars and not others. Lots of variable there too. One has to make an "educated decision" based on what they learn about the modification in question (from any and all sources), pick through what they "learn" and decide whether or not it may be be worth trying, and then try to eliminate as many variables and one can. Basically "re-tune" the engine to try and optimize it for the change. Very often, for the average racer, good record keeping, knowing your car and it's reaction to weather changes and time slips are the only tools available to compare before & after results.
I'm under the impression that even an engine "optimized" on a dyno may not have the optimum tune-up at the track, under actual operating conditions. Again, lots of variable there with weather, air flow, loads, etc. Bottom line is the time slip or lap times.