Good grief, never cite my comments as authoritative.

@Polygnome No. Consider your high TWR booster with fuel mass X. If you instead carry fuel mass X+1, then you can burn 1 unit of fuel to gain a nonzero amount of vertical height and speed before becoming a high TWR booster with fuel mass X. (Tankage mass messes with this analysis somewhat, of course, but the general principle holds.)

@RussellBorogove Sure, you're right, but you get a high TWR booster with a worse mass/fuel ratio. And fuel needed for landing is larger, adding an other penalty on the amount of fuel to be used for the launch itself.

@asdfex The mass ratio is worse, but the increase in total impulse available outweighs that hit. I don't think the landing reserve gets any worse as a fraction of launch mass.

More impulse (also) means more speed to cancel during landing. High TWR on the other hand means short burn time and less height at MECO which is favorable for landing. I think we have to compare boosters with identical performance here, i.e. same payload, same dv. (NB, I'm not arguing here, just collecting things to take into account)

You're correct that high TWR gives you a lower and slower first stage cutoff, which is one of a few possibilities I can think of as an answer to the question.

Speed should be larger with high TWR - the booster spent the same dv, but in less time so gravity losses are lower.

@asdfex The booster spent less dv because it didn’t bring enough fuel. Think of two identical stages, one with a full fuel load, one with an 80% fuel load. One comes off the pad at 1.2:1, the other at 1.5:1. Which one gets farther?

We're talking about different things. I'm talking about two identical rockets, one with a modified engine that has more power. You scale the tanks, I scale the engine.

Mine carries a little extra weight in tanks, yours a little extra weight in engines. Remember that TWR isn’t constant over the burn. I’ll put up a spreadsheet in a while to make my case.

I think I see where our misunderstanding is now. You're right -- for two boosters with the same gross delta-v performance, the higher TWR will have a higher net delta-v after gravity loss (and thus higher velocity at MECO) -- but that's not "identical performance" to me. I got too hung up on my point, which is that enlarging the tanks to drop liftoff TWR gives you yet more net delta-v.

Stage ∆v is from the rocket equation; vertical loss and net is calculated as if we're going straight up, which is obviously wrong, but simplifies comparison.

Sorry 'larger height and lower speed'.

I bet that’s the key to the answer to my original q, but I don’t know enough about the reentry/descent/landing calculus to be sure.

Hmm the fuel-fat one gets a lot higher, doesn’t it? Which means they aren’t identical performance from the upper stage’s POV.

But significantly more challenging for descent and landing. Except more specific drag....

I just tried to get something reasonable out of flightclub.io. Something's wrong with my settings. 20% more fuel give 15% more dv, that doesn't seem right. And the fuel mass change rate doesn't change with the amount of engines....