I have all three of those rifles, but not in .204.
M51 stainless in 6x45, 1771 in .17 hornet and Sako in .223. All with a 20" barrel,
I have three gripes with the Cooper, it's much heavier than I expected, the bolt is noisy, desticitive click when it cocks, and the safety clicks as well, I have a Cooper single shot in 6x47remington and was expecting the M51 to be about the same weight it's 1.5 lbs more.
Like the Sako a lot, no real complaints, other than I like the Sako vixen 461, more than 75,85.
The Sako will hold six rounds down, so 1-2 two more than the others, if that's important.
Love the Anshultz, a very accurate well balanced rifle, it's a bit heavier than the Sako, lighter than my stainless M51. Considering getting one in a second caliber.
You may want to concidered the CZ 427,in .204 I owned one in varmint .204 for a while, had to bed it wasn't much better than 1.5" to start, but was a good working rifle, once a bit of work was done,