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.
