re the magnum cartridges on the Dillons, I reload .338 win. on my 550 with good results, and this was with no previous rifle loading exp.
BUT, I essentially used the press as a turret press, b/c my powder bar would not handle 75 gr. of cylindrical RL 19. Simply used a funnel with a bloop tube with scale-weighed charges.
You will need a "magnum" powder bar if you want to reload 7 mags, 300 mags, etc. progressive style. Not that big a deal though.
Maybe I am stupid or inept, but I *have* spilled ball powder all over the place a few times when reloading .223, b/c the powder die seated on the mouth of the case rather than the shoulder.
Lee, Hornaday, and RCBS and Forster make good presses I am sure. I will never know, though b/c I have have ZERO complaints about the 500.