Back in 2007 I decided to compare the P5 and P5C both in specifications and in comparative shooting. For what reason I don't remember. I made some measurements and then shot them together, switching back and forth frequently from one to the other. The entry in my range notebook reflects my purely subjective impressions --which are worth absolutely nothing, but here they are:
With WWB 115-gr. ammo the P5C was surprisingly faster in recovery back on target. The P5 shifted more in my hand, tending to whip the muzzle. Both were excellent performers but the P5C felt slightly better in recoil. This seems counter-intuitive because the P5 is heavier overall and in particular has more mass in its recoiling parts to absorb and even out the recoil:
Slide ass'y P5: 286.5 g. P5C: 267.7 g.
Barrel & block P5: 150.2 g. P5C: 141.3 g.
Total P5: 436.7 g. P5C: 409.0 g.
The difference is 27.7 grams, just under one ounce of mass. Thus the P5C probably has a higher slide velocity, which might be expected to cause snappier recoil impact (and may have a shorter service life if one uses ammunition more powerful than WWB or similar).
For this reason I attributed--tentatively--the superior shooting "feel" of the P5C to grip shape. The P5C has a straighter backstrap that is easier for my arthritic hands to hold firmly. The P5 has a concave curvature at the web and is longer front-to-rear at the fullest part of the backstrap--which for me is harder to hold.
A slight disadvantage of the P5C is its shorter barrel, 3.1" (79mm) vs. 3.54" (90mm) in the P5, for which a penalty of about 25 fps. is paid in muzzle velocity. (That doesn't bother me particularly as I don't regard 9mm as an adequate caliber anyway.)
Far more important, in terms of reliability both guns were subjected in their development to very intensive and strenuous impartially-conducted testing and trials, and any bugs that appeared were worked out. The P5 successfully passed the German police tests of the 1970s, and the P5C was victorious in the British MoD trials a decade later. This speaks very well of both models --their performance far surpasses any factory testing ordinarily done to purely commercial pistols. The P88 and S&W-made PPK/s are unfortunate examples of the contrary.
M