Seems like you should go by the manufacturer's sizing recommendation. Though they aren't always correct. But you'll know if you try the bike first.
Might help to know what type riding you do or are wanting to do with the new bike. I don't really hear you complaining about your current fit, though the bike seems small for you. But that might just be that it's not my style of bike or cycling.
For your leg length difference, is this self diagnosed? Have you gone to find out why? Sometimes it's just that people started holding their hips funny and it can be corrected with physical therapy.