The standard advice I see on Pradopoint is change injectors at 120K km, so 75K miles, if you are not watching for wear via Techstream, and a sensible figure to factor in to maintenace cost estimations. Never seen 40K mentioned. I changed mine at 150K miles, but they looked pretty worn on Techstream (a couple were +/- 4.0, one was +/-5.0 on the fuel trims). I feel a lot better for having done it.
The intimation on PP is fitting perf chips seems to speed up injector wear, but it's not the only factor.
Some people seem to have no bother at all. There was a guy who used to post here who'd done more than 250K miles on the same set of injectors, no bother. Another guy here local to me bought an LC4 with about 110K miles on it, and when I hooked up Techstream the injector values were +/- 1.0, so not at all worn.
Quite a few cars seemed to get new injectors under warranty and perhaps that was one of them.
I'd get yourself a Techstream cable and software from ebay and check your injectors every 5 or 10K miles and watch for them wearing. Personally I think I'd change it they were getting close to +/- 3.0, but thats just a number I've seen quoted as a sensible limit.
Next thing I want to do is clean my EGR valve and probably fit a restrictor (blanking plate with a small hole drilled in it), which seems to be regarded as good practice.