never rode 1 x 11 – doesn’t this run out of gears on the flats and downhill ?
Yes/no/maybe. It’s highly subjective.
Running a SRAM 10-42 cassette you get a 420% gear range, you then just pick your chainring size to prioritise whether you have a super low crawler gear, or retain some top speed. My first proper MTB, a 1990 Marin Muirwoods, had a triple chainset (28/38/48) and a 12-28 cassette, which equates to a 400% range. So a modern 1×11 setup has a wider range than an old school 3×7…
There’s plenty of people out there that have been running 1×10 with an 11-36 (327% range), or even 1×9 with an 11-32 (291% range) happily for years too. Hell, some people even ride Singlespeeds!
The point is, only you can decide. Last time I had a triple, I only used the 11/13/15 cogs whilst on the big ring when I was on road, pointing downhill. A situation where I’ll happily freewheel to be fair. So I’ve got a 30T ring with the 10-42 cassette on my 29er, which gives me a usefully low winching gear (though at times I’ve wished for a 28T on some steeper climbs) and a top gear that’s still totally redundant off-road anyway.