Whilst I'm right on the cusp between sizes at 5'7 I've tried 3 different make/model mediums in shops and on all of them the staff had said I'be be better off with the small (nowhere's had one in stock to actually try) and the reach does feel that bit too much but I'm looking for a 2nd hand bike and smalls virtually never come up but there are loads of mediums available (one in particular at the moment).

If I take this bike as an example
https://www.halfords.com/cycling/bik...adventure-bike

the difference in reach is only 9mm ... is that the figure I should be looking at and if I swapped the stem for a 10mm shorter one will that in essence do the same thing or are there other differences I'd notice and would you just wait until the right size comes up .... that said I've been looking for months and have money burning a hole in my pocket at the moment.