I've been loading my 10mm exclusively with CCI300 primers since I've had it, but a couple weeks ago I discovered that Bruno's had Winchester Large Pistol primers in stock for $30.75, about $4 less than I was paying for the CCIs. Bought some and tested them, in 2 separate batches.
Today's, more-reliable*, tests were of 25 rounds of each, shot in 5-shot groups, all chrono'd (but I didn't get 25-each readings due to hurried initial chrono setup) and shot from a rest at 10 yards. The basic load is new Starline cases, weighed charges of SR4756, and Montana Gold JHP155s. Today's load used 10.8g. The average velocities (with screens centered at 10 feet) differed by ONE foot per second (1365 v. 1364), statistically insignificant by anyone's definition. I measured 24 shots with the CCIs and 20 shots with the WLPs. The WLPs produced a standard deviation about half of what the CCIs produced, 10 v. 18FPS, and the WLPs' average group size was about 30% smaller than that produced by the CCI rounds.
Friday's test results were somewhat reversed from today's, but with all 9 groups combined, the WLPs still produced smaller average group size and lower standard deviation.
I'm staying with the WLPs.
* that is, a larger sample size and more-pleasant shooting conditions