Man, you 'My shooting ability doesn't fade' voters are real men! My answer was after 100 rounds.
There for a year or so when I was going for accuracy and doing 'drill bills', I would take my Dan Wesson 22 revolver and some centerfire handgun, either a CZ, a 1911 or Taurus PT99 to the range. I would shoot about 50 rounds of the 22 then switch to centerfire. Generally, I'd take 100 rounds of ammo. First 10 rounds was slow paced fire at 25 yards. Then in no particular order I'd do double taps at 25 yards, double taps at 7 yards, 3, 4 or 5 round rapid fire at 7 yards, one shot to each of two targets at 25 yards, one shot into one target, then another, then back to the first one. Then some 50 yard target shooting and 100 yard gong ringing. Then I'd go back to informal rimfire plinking.
I love the 45 ACP cartridge and I love the 1911 platform but I must admit that I did much better shooting at the longer distances when I had a 9mm with me. Also, the few time we started off shooting centerfire at longer distances, after a short warm up, my groups were better and I was more confident in them than when shooting at longer distances after a lot of shooting.