I'm not a big fan of creep feeding. It's added expense at more cost per pound of gain and I've always bred for genetic gain to begin with. After weaning it may pencil out but before weaning I just don't see it.
These are the numbers I've worked with. I get a ninety pound calf and expect it to wean in 205 days at 600 pounds. So 510 pounds of gain in 205 days is almost 2 1/2 pounds of gain a day average.
With creep you might push it to three pounds. My 2 1/2 pounds a day is done on fixed inputs that are going to be static whether I creep feed or not. The only way I'd need to creep feed is if I weaned early and failed to use my milk machines designed by evolution to put weight on the calf.
So the question becomes... is creep feed, including ancillary expenses, worth a 1/2 pound of gain until you sell the calf at what age and weight? The diminishing prices per pound of calf need to be figured in as well.