Issue is in many guns the lighter bullet wont cycle the slide without recoil spring reduction, which often comes with reliability issues. So to get good slide speed, a heavier bullet does that at lower vel with the bonus of less blast. The 165 @ 775fps could almost be shot without earpro, almost.
My experience with Glocks is all gen3, which I think is the best choice for aftermarket support and tuning. I moved from Glock to Tanfo for Production in 2016.
I've never met anyone who knows what they're doing that's shooting Glocks in minor with anywhere near an OE recoil spring, so that's a non-issue. Sevigny was cutting coils off #11 springs back in the day. #12-14 is the normal range. I've always used #12's in my 34's, and I go down to #10 for steel ammo in the 34's. I use #9 springs for all ammo in my Tanfo's.
Driving factor for recoil spring weights is how sights return. If that part is right, function should not be a big deal. Of course Tanfo's are vastly superior to Glocks in terms of slide/gun mass, but that's another topic. Glocks also don't have barrel/slide lugs to lock up, so no concern there. I had some problems with #8 springs in Tanfo's in that regard.
Slide cuts weren't legal in the old Production rules, but they are now. So you're going to add forward serrations, and presumably take a little more mass out while you're at it. That helps handling and stability, but springs are probably going to be the same as before.
My Production load is normally a 147 or 150gr coated or plated RN bullet with ~3.25gr of WST or 320 at 1.135. My steel load is typically a 115gr coated RN bullet with 3.40-3.60gr of WST or 320 at 1.100. That's more like 110PF, and all my guns run it 100%.
Because I changed Production platforms before the rules changed, I never got into lightening slides on my 34's. I carry 19.3's. Slides on those guns are ~10% below OE mass. They run everything from +P HST down to 110PF steel ammo 100% on #14 springs.
As a side project, I built a 17.3 last year. Wanted to see how it would compare in terms of balance and overall performance to my Stock 2's. I have a bunch of G17 slides that are reduced 5-10% from OE mass. The 17.3 performs similarly to my 19.3's with a #10 spring.
For SCSA and hanging steel in general, I like a bit more velocity in a super-light round. Without going into a lot of detail, this is what I was basing my suggestions on above.
So bottom line, there's lots of misinformation out there. Do your homework, do what you need to do to make your stuff run 100%, and get after it.
