I would think that IMR4451 would be a better choice than IMR4166 with a .30-06 or a .270 since both of my rifles in those calibers really like IMR4350.
IMR4451 is the Enduron equivalent to IMR4350 according to IMR's data sheets.
IMR4166 is the Enduron equivalent to IMR4064 according to IMR's data sheets.

As for using IMR4166 in a .223 Rem, I would suggest trying IMR4166 with heavier bullets.
For lighter bullets from 52 to 55 grains, powders in the H335 and N133 range seem to shoot much more accurately in my rifles.
I don't have a bolt action rifle in .223 in a fast twist barrel so I haven't tried shooting heavier bullets in the 69 to 77 grain range in a bolt action .223.

For heavier bullets, my Les Baer .223 with a 1:8 twist barrel likes IMR4064, Varget, N140, and H4895 with 69 and 77 grain bullets and it should also like IMR4166.
I haven't tried IMR4166 Enduron yet but that is on the agenda for the future with the Les Baer .223 with 69 and 77 grain bullets, probably sometime in the spring.