Thanks for all your valuable input!

(Leaving the math talk aside – though I’m still following it with interest. )

I’d never really gone beyond some basic thoughts on the topic, but you’ve opened up a whole new world for me!

I’d probably do fine with a 1x8, but looking at the bigger picture and everything you’ve said, a 1x10 sounds like the best option.

I’ll keep following the thread – but please, don’t wear yourselves out!

Yes, 25-27 mph is the maximum for me with bags. Thank you, I’ll keep that in mind!

Of the options you presented, the 1x10 gets you more on both ends, and having 10 cogs instread of 8 probably means your spacing between gears in the middle is very similar. Based on your description of your riding, you might never need the expended lower end, but you probably aren't losing anything by having it.

I like this chart for comparing gear inches between different setups. https://www.bikecalc.com/archives/gear-inches.html Just enter 38 & 40 for "chainrings" and 11 & 48 for sprockets plus the rim and tire size. Click "calculate" and you'll get a chart with columns of gear inches for any gear, easy to do comparisons.

Yeah that gear selection depends what cadence I feel like but similar speed. Can hit 45kph some days, prevailing tailwind in the morning. It might also be slightly downhill on the section I’m thinking of as it goes along the side of the Thames in the direction of flow. It also has a dedicated bike lane and 20mph speed limit so going noticeably quicker than the cars is always fun.

Just do simple ratios and decide which gives you the highest gear.

The Acolyte bike OP describes has about 3:1 overall ratio and a low gear about 1:1. This is ... okay, could make do but seems like we (except for the single speed enthusiasts) mostly agree he'd be happier with closer to 4:1 overall and one shift under unity, especially considering he wants to do both recreation and utility riding. I ride in a fairly hilly area with a bum ticker and don't have needs greater than a 11t-42t cassette. I wasn't going to recommend him the 12 speed 50t+ MTB setups.

For those talking about shift sizes. The Acolyte cassette follows a typical MTB +15% shift pattern until the lowest two bailout shifts, which are +25%. Shifts of +25% are somewhat uncommon nowadays. They seem to have been common enough in the bike boom days as "alpine" gearing. But they do show up from time to time for a bail-out. Shimano's first 1x11 speed generation had a cassette where the granny shift was 37t-46t.

Just to sum things up, I had an unexpected chance to test a 1x8 setup this morning.
Although it wasn’t the Microshift Sword but rather an old Shimano something, it had the gearing I was looking for (38t with 12–42t).

On the drive lane, I easily reached the 7th gear on flat terrain with a tailwind, and the 8th on short slopes (about 150 m long). This makes me think that on longer slopes, I’d probably run out of gears.
It convinced me that, for my riding style and on a gravel bike with a more aggressive/racing position than the one I tested, the 1x8 would feel limited.

This basically confirms what most of you have been saying: it’s a personal choice, but if you tend to push more on the road, the 1x10 is probably the best balance to have.