There is no way that a .270 could ever be considered to be inadequate for whitetailed deer. If you have one, its more than able to do the job.

That being said, the most effective and devastating round I've ever used for eastern whitetails is the .303 British. I started hunting with a No 1 Mk III SMLE, using 180 grain CPE bullets (no longer made), and had bang/flop performance on my first 4 deer and my first moose. This may have been as much to the credit of the bullet as the cartridge, but I've spent much of my life trying to get a cartridge/bullet/load combination to equal its performance.

Admittedly, many of the old guns themselves leave something to be desired, but I've recently acquired a Winchester 1895 and a Globco 555 in .303 that I hope to give a try in one of the upcoming seasons.