Which Groupset?

Shimano do an 11-34, which isn’t far off.
The Force level 11-36 cassettes are really nice, other than being an absolute arse to clean if you get it mud and grass in them.

I've been using a mix of 11 speed SRAM or Shimano cassettes and chains on my bikes for ages and can't really tell the difference.

Shimano do an 11-34, which isn’t far off.

They do, and I have many. The spacings between the gears is a bit odd on the 11-34 cassettes, but I have no complaints in practice.

The Force level 11-36 cassettes are really nice, other than being an absolute arse to clean if you get it mud and grass in them.

Again, no complaints so far. I've got them on the wheels for my as-yet-unraced Cyclocross race bike.

I've used two versions of SRAMs 11-36 and they're definitely not as nice as Shimano cassettes but they function fine. I've since moved to Shimano MTB cassettes anyway where they're pushing the shifting limits even further. The missus now has one of the 11-36 cassettes on her road bike. I may have one on the turbo or it might be the OG 11-28T it came with, I can't remember. Done lots of miles on them anyway. I'd previously used a SRAM cassette on 10spd DA groupset for Pyrenees and Alps and that also worked fine, if a little rougher than Shimano but then they didn't offer a 28T at the time IIRC.

11 speed interchangeability is great. I’ve got a a shimano cassette on one set of wheels, SRAM on the other and Campagnolo on the turbo. Without checking I wouldn’t even be able to tell you which cassette was on which wheels

Verdict?

It's 1x.

Darn, now the 172.5 is also sold out.. Can only see 165

That's the best size.

Both crank arms are shared between 1x and 2x (product number FC-RX600), so you could convert it to 2x if you can find the rings. Bit costly though.

THAT is a really good shout, I could convert the one I already have..

Edit: impossible to find

You already have some? I wasn't going to suggest above because it's like buying 2 sets of cranks, I think you can get after market rings though.

I have one on another bike, but since this is all for just one trip, I could swap it, convert it and then redo the whole thing afterwards.

Who makes them? If it's the same as the 1x it will come out more expensive than a whole new crankset and as you say, 165mm isn't bad

Just think of the ruts! 165 is the future

My gravey cranks ain't GRX but they are 2x 165mm.

On the subject of cassettes, I've been having good results with Miche 11x light with an Ultegra group. I have no need for an 11 tooth which limits options in Sram and Shimano. Miche gives the option of custom ratios too.
They aren't particularly tolerant to being out of line, so you have to keep on top of adjustment, but silent and slick when you do.

Does anyone have experience of running 11 speed shimano cassette with a Campagnolo groupset? Seems like it works OK from what I've read on various online forums but LFGSS hive mind reigns supreme

Miche 11x light

Good shout, 12-29 looks ideal for me and not too spendy either, cheaper than Ultegra.

Does anyone have experience of running 11 speed shimano cassette with a Campagnolo groupset?

Works great. Might go as far as to say it shifts better than with the original cassette.

Campagnolo Chorus 11 speed groupset with Shimano 105 11-28 cassette (and Shimano Shimano CN-HG701-11 chain).

12-29 looks ideal

That's what I've got, with a 52 36 up front, covers me for everything I've encountered so far

Cheers man! I’m going to order some light bicycle wheels with Shimano hub but run with chorus 11 speed. I see myself in the future perhaps going to Di2 so the Shimano hub and affordable cassettes seems a good move

Having started to tow my son in a trailer, for increasing distances and with a view to go longer and hillier I am spending some time considering acquiring some additional gears/gear inches. Bike is an oldish genesis vapour, specs as in link, 10 speed tiagra 4600, currently running a 12-30 rear cassette and 46-36 crankset and when towing trailer am only in bottom 6/7 gears.

https://www.thebikelist.co.uk/genesis/vapour-2014

Options considered so far would seem to be
33/34 tooth inner ring
Chancing a 32 or 34 tooth cassette (possibly with a roadlink?) and new chain
46-30 Sub compact crankset e.g. miche Graff duo or grx (which might need a new front mech?)

Which/which combination is likely to
1:work
2: make an appreciable difference
3: be relatively cost effective

A gear inch calculator seems to suggest about a 2-3 inch gain per option, which is about 1-2 gears? Should I just get stronger/buy a new bike/s, have I missed an obvious/cheap solution. 46-12 is plenty big enough for me when unloaded but wouldnt want to lose too much top speed while this currently my only bike.

On both bikes I've just gone to bigger cassettes because it's the cheapest, easier way to get lower gears. Subsequently went to gravel P2M on the gravel bike but that's a bit of a luxury and my missus has my old P2M with Compact cranks so that made her road bike nicer.

A good old triple would make sense?
Any mtb triple 26/36/46 up front.
7 speed stuff is cheap.

Good price on a subcompact 2x crankset for anyone riding 175mm?