I’m between sizes as well in most S-M-L sizing on anything. I essentially need the L length, but M fit. And in most stuff, I’ve found I’m happier in M. For shoulders, an L on me rides up, and I have to pull it down. Buuuuuut, that’s me.
Does a friend/teammate/acquaintance/tinderhookup have a pair of S you could wear for a game or two? Much easier to decide once you’ve worn both, but it’s also a mindgame because different pads fit differently.
If the M feel good, stay there. A lot of the differences are negligible, and sounds like you’re mostly concerned because of Bauer’s chart, as opposed to them being uncomfortable. At the end of the day, you gotta go with what’s in your heart and what feels right to you.
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My solution would be to buy a pair of S used somewhere, then sell the pair that you don’t want, then buy an upgraded pair because now you know for certain what size you need, and you spend a whole month overthinking selling and reselling and buying and end up in pretty much the same spot, but $150 poorer because you also bought a pair of gloves, because you could get them shipped for free along with the shoulders.