I built mine 25 plus years ago and started with Nosler 50's seated into the lands about 0.005" and worked in and up on the length and charges by 0.005" and .5 gr increments.
I was getting near 4200 fps with the 50's and Norma 204 powder but I never got much below 3/4" groups. Piss poor Ruger action, and a heavy Douglas SS #7 taper 26" barrel. Never could get the action to bed right and the action was to limber for that heavy barrel. Finally shot out the barrel working on loads.
Sometime this year I will have Sharp Shooters Supply make me up one for my Savage 110.
It's a good cartridge. You'll get about 150fps more than a Swift at the same pressures and the cases will last a dozen or more reloads. I usually did 10 reloads and tossed the cases just to be safe.
Use 243 cases, don't use 308 cases and you will get another 10 thou or so added length when you neck down. I also used 6mm Rem, 257 Roberts and 7x57 case just for the experience. You need to be careful and go through a lot of gyrations if you do, though.
Don't hot rod it. 10% less pressure and you lose only 5% velocity and get 100% better accuracy and case life.
I've looked at the 284 case for a long time and have a long throated standard 284 just to seat out longer and a 6mm-284, that needs a new barrel, I liked very much.
Do you lose many cases necking down that far? I'm waffling between the 22 cal and a 6.5mm or both???? Haven't tried the 22 cal mostly because of the overbore problems, but with a 32" to 36" barrel it should work out OK. Let me know the straight scooby-do, hey, I'm one of the boys. : ) What do they call that, a Valkyrie, something like that??