What controlled test did you run and what were the results? I sure would like to see a quantitative comparison.
Just to be clear, I performed no "controlled" test. I tested GL1 and several other gear oils in one of my freshly rebuilt 5 speeds in my street car and in another freshly rebuilt 5 speed in my DSP autocrosser.
I ran the street car ('74 1300) in varying conditions from cold mornings to hot afternoons over a period of about a month. Then changed to Redline MTL and ran the car for another month in similar conditions. I wanted to know exactly how the two compared in synchronizer performance in varying temperatures.
For my DSP autocrosser I tested at different events in varying temperatures a number of different gear oils. I used Redline MTL as a baseline and included MT90 in the test. The other oils tested (that I can remember) were Pennzoil Synchromesh, GM Synchromesh, Royal Purple, Castrol Syntorq, Mobil One 75/80(?) and a couple of others I don't remember. I also tested 10w30 synthetic motor oil and ATF.
I have also had a number of my transmission customers run GL1 and various other gear oils in their road race cars.
I have also run GL1, Redline MTL and synthetic 10w30 engine oil for extended periods in my street X's.
What I learned from running different oils in my two cars is that GL1 is very temperature sensitive. It works poorly in low temps and high temps. It causes excessive synchronizer wear and low synchronizer performance. It will coak up and break down at very high temperatures. It has poor moisture resistance and varnishes badly with age, contamination and heat.
I also learned that MTL and MT90 have excelent low and high temperature performance. The lowest synchronizer wear and highest synchronizer performance. High moisture resistance and virtually no coaking or varnishing of any kind.
In comparing the other oils, GM/Pennzoil Synchromesh were 2nd best to Redline. Then everything else more or less tied at 3rd place.
To make full disclosure; Redline was a sponsor of the Pro racing team for which I crewed for nearly 10 years. In that time I had a number of chances to talk with Redline engineers and had access to their full line of products. I have maintained that relationship ever since. I learned a lot from those guys.
While I don't have controlled test data I have probably had more X1/9 transmissions apart on my bench than anyone else. I know what they look like after using the factory fill GL1. I know what they look like after 10+ years and 100,000 miles of Redline MTL. I know what they look like after 5 seasons of autocrossing with MTL and I know what they look like after 20+ races in a Production road racer. So I probably have more real world experience than anybody as to what works. I did the above testing when I began to get serious about building these transmissions for customers. I needed to know for my own peice of mind.