While the 5107 has got the former auto 315 caliber with a 21.600 beat ratio, the new 5127 has got a 28.000 beats producing caliber 324.
I would rather prefer the old movement, although the second hand should (should as I do not own one) run less smooth than the 5127 one's.
Design wise the updated 5127 winns over the 5107, as the 5127 bezel is a bit too flat to my taste.
But this model is a good example for Patek's policy not to magnify every model: no chnage in size between them.
I all these are just marginal differences and an owner of each is and can be very lucky to possess it.
A very, very fine watch ...
Regards
Moritz