Re: .22-250 or .220 Swift
One other consideration no one else has mentioned and that is feed reliability and reload ability for rapid fire in competition. If you can find a rifle suitable for a clip slot and magazine capability to take five rounds you could use this rifle for highpower competition. Best platform for this is the pre war Mod 70 as they came with clip slots.
Thusly 22-250 is the way to go as it will feed rapid fire and you can reload it in mag using stripper clips. Actually a 03A3 would work for such a project gun.
I had a Wilson Arrow which is an improved Swift and while a fine gun was useless for rapid fire competition.
With a good tube and good loads 600 yards will not be a problem and I wouldn't mind taking 80 gr. to 1000 with 22-250.
You might as well get enough rifle at the first build to do the job all the way.
If you could find a pre war Mod 70, all you will need is a barrel.This is like the pic of the fine specimen above. A No 5A 26" barrel contour, 8 to 8.5 twist rate in 22-250 and you can play with the big kids.
This barrel contour will allow for two set backs which is cutting threads off and cutting a new chamber.On second set back you will still have 24" barrel and assuming you clean it often should last you 7500 rounds.
If you order your own custom reamer to min dimensions you will also get long brass life and a reamer is good for at least 25 chambers. If you get a rougher reamer as well good for a hundred chambers on the finsh reamer.
The Pre war with clip slot can also be rebarreled to 240 NMC, 243, 7/08/260,308,30.06, 280, etc etc and no expensive rework.