The 5107 has got a flat bezel and the 315 movement with a less stressful beating 21.600 beats.
The 5127 has a convex bezel and the "modern" 324 movement with a higher beat ratio of 28.000.
I personally prefer the 5127 case, but the caliber 315 as it beats less stressful.
Having said that: one should be happy with both of them.
Regards
Moritz