How wild?
600 is nothing. You can have 100 ES and still shoot plenty well at 600 yards. I shot a 1/4 MOA 5 shot group with a 60ES at 600.
I feel like your wants, in comparison with the 22CM cartridge itself, might not be the best fit. Or you might have to re-evaluate them slightly. If you've done all this group shooting at 100 with tons of 1 MOA decent sample sized groups and haven't even taken it to distance, I think you're off track personally. You're trying to create a unicorn load, to meet an essentially very easy goal. Small groups and slower speeds, or fast speeds and slightly larger groups will both still hammer at 600 yards. Just shoot it IMO