The .30-06 is still a good choice, but smaller cartridges work very well with the right bullets. Have seen elk killed neatly with chest shots in cartridges from the .22-250 up.
Must admit that I get a little weary of the constant elk-cartridge debates here and elsewhere. I grew up in Montana when the majority of elk hunters used the .30-06, partly because there were so many "affordable" military-surplus 1903 Springfields were still available. Nosler Partitions were the only controlled-expansion bullet available back then, but had to be handloaded--unless you owned a Weatherby, since they started putting Partitions in the factory loads in the early 1960s.
Consequently most hunters used 180-grain .30-06 factory loads, and they worked--partly because back then Remington still made the original, heavy-sidewall Core-Lokts. Did know one guy who used 220-grain bullets, but he hunted heavy timber.
As I've patiently tried to explain to my brother and his circle of elk hunting devotees for at least the last 10 years when they respond "You use WHAT on elk?"
I tell them to start first at the bullet and then work backwards towards how it's delivered.
