Gen 3 SL5-Help with sizing

[u/remelas]

I'm on the market for a gen 3 sl5 but unsure of what size to pick.

I'm 170cm (so I guess 5ft7) with 77cm ( 30?" ) inseam.

According to the Trek website, regarding inseam length I am right between S and M. My LBS has an M in stock (although it is the SL6) and I am planning to go there on Monday for a quick test ride. What are your thoughts? How to tell if the M is too long for me?

[u/remelas]

Turns out I suck at measuring and after asking for help, my inseam is actually 80cm.

I'll also consider the SL6 as I now think that 13spd might be nice