I use Winchester primers in both my .38's and my .357's but I don't load to max velocity in either one. Most of what I read and have been told is that magnum primers are needed to ignite stubborn powders that need a more uniform burn to function. This seems to be why 2400 powder makes a so so .38 but makes a great magnum. So if you are trying to push your loads to the max listed velocity you will need the right primer. So how does Win do it? My two cents says it does that good at both but best at neither kind of deal. Or at least not best at magnum max velocity listings. And I don't know about adding 5,000 psi, that sounds like just a bit much.