If you don't like the PM opening now, I doubt you'll like it later.
Style-wise, I think PM is a little more versatile than speedy. Speedy always looks casual to me, but a PM you can dress up or down. The 35 size looks like a travel bag to me too.
Since Speedy b 35 and PM are very different in size, I would also consider which size you would use more often. If PM is better but you don't like PM's s-lock, get a bag that's similar to PM size with an opening you prefer.
I have a speedy b 25, and I'm thinking of maybe getting a PM. Other than the s-lock, are there any other cons you feel about the bag?