71" eh..so that is...5'11"...I would go MD 17.5". The reason is my friend who is 6'3" found a 19.5" LG too big....he switched to a 17.5" M after and its perfect now...consider that you are not even 6', you shouldn't go with large. Your shop might says large...but test it yourself, see if you can pull ur front wheel off the floor on a flat surface standing at least 2" and the best 5". It also depends on what bike you are getting...if a FS, MED for sure...don't even try large.....top tube length can be fixed with stem, bars and pedal position can be change with seatpost, and crankarm length....