I'm that size but just a shade closer to 32" , went to ride a med and lg in all test rides.What size would I be on the Dragonslayer? I'm 5'10" 33" inseam.
Either works for me on some brands but I'd say lean to a large if in doubt. Years ago the trend was most leaning to the smaller cockpit and sizing but newer frame angles and trends change that.
I think if I was slugging away at long commutes or high mile bike packing trips, I'd favor the large in my case but it's not a Jamis. Each has it's own personality and 'sit'. Some bikes differ very little on med to lg and in all cases (as/if needed), the adjustment criteria is used to fine tune such as seat rail, stem length or angle etc.... A good LBS can assist to show you how either size would better fit with those variables and one will probably require less adjustment and be a closer 'real' fit. I felt good on a medium Marin and the seat post wasn't at an extreme extension, reach felt right etc.... I'm 56 and think that played a part. If I were more aggressive in high spirited riding and speed, I'd have went to the large. The Jamis DS was high on my list of 2 or three bikes to choose from.