GRX 2×11 Vs 2×12 and Specialized Diverge sizing

Two questions,

Any noticeable difference between 2×11 and 2×12 GRX assuming same level (800 series) components? 12 speed MTB seems a bit more fragile than 11 but sometimes that could be attributed to just bad luck or clumsiness from my part.

At 5’10/177 Specialized put me on a 56 over a 54. L Going to get advice on this from a decent local shop but what’s your opinion/preference?

I am same height and on a 56. I have Roubaix too which is 54, the 54 Diverge wasn’t big enough.

i am slightly shorter, at 5ft 9.5 and am on a 54, which fits perfectly

Geo has probably changed, but at same height with short ~32″ cycling inseam, my old 56cm 2009 Tricross Singlecross seemed to fit me really well… Albeit I was rarely using it for anything more than ~5 mile each way commutes back then.

I’m thinking of a new gravel bike build

My thinking was that I’d go 46 30 chainset and 42 11 out back. That would give more the low gear i want. This was 11 speed grx

Not sure whether that would work with 12 speed. 1×12 might work for me with MTB cranks. There seem to be 3 shimano 12 speed blocks with largest sprockets of 36, 45 and 51. The 36 isn’t low enough for me with a 30 up front. But i can’t see the 45 would work 2x

So for me 11 died looks better, with 12 also just being a touch harder to get running well

With 2x  11 speed Grx you can go to 40t at the back with just a tweak of the b screw.   I’ve been looking for a 10 or 11 to 40 12 speed cassette.   I don’t think one currently exists.  That’s enough for me to stick with 11 speed.

I’m 5’11” on a 56 Diverge with an 80mm stem, 90mm stem on my 56 Roubaix. Wife is 5’7″ on a 54 Diverge with an 80mm stem but trying a 70mm.