I'll chime in
First of all, i'll tell you about the challenge of accurately testing an injector. There are hundreds of companies that test/refurb injectors and they all use different equipment and testing fluids.
I use an environmentally friendly degreaser just because i don't feel like using dangerous chemicals in my home garage, But others use other fluids and all these fluids are different from real gas. Even the gas at the pump will have different fluidity in different parts of the world
So the same injector will show different results tested with different fluids. That's why the manufacturer suggests that your 6 injectors should flow equally with a 2% error margin. They also suggest the flow rate but it's just a guidance.
It is important to have balanced injectors and less important to have that flow rate exactly as mentioned by the manufacturer
Both M20 and M50 injectors are considered 17 pound injector.. it's about 160 cc/min. In real life you will have somewhere between 150cc/min to 170 cc/min. That's why we flow match to get a set of 6 injectors that are within 2% of each other (per mfg recommendations)
The difference is the spray pattern and since M50 injectors have better atomization (they mix air with fuel better in the chamber) you will get bigger explosions and more energy generated from the same mix of fuel/air.
What matters to your engines is keeping the stock Air Fuel Ratio in a stock configuration. Since vehicles operate at different altitude and use different fuels, the DME is able to tune the ignition to maintain a stable AFR
I don't remember precisely, but it can adjust about 2-5%
I test injectors in pulse mode and i can see how challenging it is for a DME to maintain the same flow rate on 6 injectors under different RPMs .. needle type injectors especially (M20 blue tops or ETA gray tops)
M50 injectors do a way better job at keeping a stable flow rate in different modes. I test them at way above your car's RPMs sometimes just to see how well they perform and Green Top M50 injectors are just superior.
I scrap about 20 injectors a week and a lot of times i put them to stress test... FOR FUN
I run them at 7-8 of fuel pressure at 10k RPM to see where and what injectors will fail... and i'll tell you that the stock M20 injectors are just Sad to watch, especially the ETA gray tops.. those are like watching 80 yo old grandpa racing on a sport bike in the canyons
And lastly.. experience... I've sold over 1000 injectors last year just for this upgrade. Shipped all over the world to people with M20 engines that wanted the M50 injectors. There are people running this upgrade at different altitudes and different climates
I've had 0 complains so far and 0 issues testing emissions on any of those cars.
If any of you purchase this upgrade from me and feel that you are not satisfied with the results, i will exchange that set for a stock rebuilt M20 set without charging you any extra. I used to remind people about it all the time, but stopped doing it because everyone seems happy with the upgrade.
Here's one of the latest reviews about this upgrade
I had a request for a set of 6 stock M20 715 blue top injectors this weekend and i knew i had 12 of those and was confident that i could pick 6 good ones out of 12..
Well, i scraped 10 injectors and was able to keep only 2 out of 12 that i had. Failure rate is just ridiculous on those, especially if the car has been sitting for over 2-3 months