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The above is very true.
However, to answer your priginal questions, going with a lighter spring will generally cause the weapon to have less muzzle rise because the recoil spring transfers less of the slide's momentum into your hand during the relatively long period while the slide is in motion. And, because it is not moving as quickly when it returns to battery, you have a correspondingly-smaller "dip" of the muzzle at that point. However, the downside is you end up with a proportionally-sharper recoil impulse at the very end of the slide's travel because the slide is going faster when it knocks against the frame. Fortunately, because this occurs over a very short time period (one instant of contact), the overall affect is less muzzle rise because that energybinstead goes to displacing the tissues of your hands and arms. Of course, I would take that over a heavy spring and higher muzzle rise, especially with mild 9mm loads.
Basically, though, you can go as light as you want--using proportionally-lighter loads to avoid extra wear on the frame--until you run into feeding issues. I have heard of people going as low as 9-10lbs.
FWIW, however, I have gotten a factory Gen3 G26 to reliabel cycle 124gr bullets down to about 800fps, and my Favtory Gen4 G21 to reliably cycle 225gr cast bullets down to about 600fps. So, you might just experiment with how low you can go as-is.
And, of course, all of this falls on a continuum, so don't necessarily expect a night-and-day difference. However, I do believe most would see a noticable dofference going from a stock spring to, say, a 10 or 11lb one.
Also, ideally, one would either add muzzle compensaion or lighten the slide to gain the full benefits of the above principles.
Finally, I can't say whether it would really be a good idea to cut the factory springs vs replacing ones on a Gen3 guide rod.