i use 12-25. I find the gaps small enough on the flats, and if i do run into a hill around here i don't need to get out of the big chain ring.
BTW i have standard front crank

Get a lot of use out of that 54-11 do you?

12-13-14-15-16-17-18-19-21-23 10 cogs. You don't need the 12 cog but it makes 39x13 a more reasonable choice.
13-14-15-16-17-18-19-21-23-26 10 cogs. You get a lower gear for bumps and stay on the big ring longer.
12-13-14-15-16-17-18-19-21-23-25 11 cogs. Best of both worlds.

with one tooth jumps through the 19 cog where that stops being significant.

I've been riding a 14-15-16-17-18-19-20-21-22-23 straight block as an experiment. 50x14 is plenty big (like 52x14 when 10 speeds meant 5 cogs). The 22 is redundant and serves only to provide a better chain line on 50 x 21 - I'd definitely swap it for a smaller starting cog to defer shifting up from the 39 ring. The 20 is noticeable but not something I'd really miss like the 18 so 13-23 10 cogs might be interesting although I'm undecided on how I'd feel about that versus 12-23 for flatter terrain or 13-26 hillier.

53x13 is a 32 MPH cruising gear and 43+ MPH sprinting gear and bigger than the 52x13 Eddy used to dominate the spring classics. You aren't a Merckx and don't need a 12 to say nothing of the 11.

I'm 50 (oops) pounds over racing weight and completely out of shape by road riding standards. On flatter terrain I don't need a gear lower than 39x23.

The best approach is to use personal experience. How low a gear do you need to avoid unacceptable fatigue climbing the hills you'll encounter? When do you keep switching between cogs because you want another between them?

Next best is to start from what you know and extrapolate. You know what sort of cadence you prefer, how fast you ride, and where things like double shifting would be annoying.

Take a look at Mike Sherman's gear calculator. It's the best because it provides overlapping (or not, suggesting you want another cog there) speed bars for each gear combination and sorts the cogs and rings when you make insertions or deletions

https://home.earthlink.net/~mike.sherman/shift.html



The astute observer would note that eschewing the fully cross-chained combinations the preceding diagram shows 34x14 and 50x21 as the only overlapping gear combinations, ring changes are likely between 16 and 18 MPH, that overlaps with pleasant cruising speeds departing slightly from flat, and a lot of five cog double shifts would result. Actually experience matches what one would predict.


Only on your postal scale.

The impact of weight on speed is at worst proportional to it when you are climbing a ladder carrying your bike. Real roads can't be that steep so the effects are somewhat lower.

Consider a 140 pound climber atop a bike approaching the 15 pound UCI minimum with a total weight of 70.3kg.

Gaining 20g as on a cassette one size bigger would drop his speed to 70280/70300 = .99972 of what it originally was or 0.03%.

The 100g difference between small and large cassettes would net 0.14%.

Even gaining a full pound or 454 grams would only make a 0.65% difference in that situation.

The impact on flat ground won't be measurable.

Bigger bike + rider combinations will be affected less.

I like the inteface and graphics better on this one:

https://www.gear-calculator.com/#

It is the only gear I use. Strava.