I have a small array of varmint rigs, .223s and one 220 Swift, but prior to owning these; I used a .243 for both varmints and deer. And before that, a 30'06. My reason for swapping away the '06 for a .243 was because I wasn't in the position to own a deer rifle and a varmint rig. Heck, I was a working student who could barely afford the gas and a range fee on the same day! Life is often about 'The Useful Compromise.'
Recoil is often an issue. Is your bigger gun making you shoot better or worse? For me, frequent shooting with the .22s translate to better shooting with my 7mm mag, but there is a down side. You can develop some inconsistency in your shooting if the guns are very different. (For me, it seems to be about triggers.) If you've been driving your five speed much, and suddenly move over to your automatic, you'll find yourself ready to clutch and waving a hand in the air for a stick that isn't there. This is precisely why some varminters switch over to their big guns before a season, and they will sure enough make a prairie dog trip with this justification in mind. For others, it may never be a problem.
In the end, there's only a couple of primary issues: 1) Cost 2) Recoil Some would make 3) pelt damage, but as Chappell pointed out, that's easily fixed with bullet selection. (I'm knowingly broadening the scope beyond the OP's specifics. Work with me here.
) I had some '06 kills where it was difficult to find entry/exit. And some might add 4) a safety consideration, but I’ll kick that to the curb straight away. Your safety considerations, training and habits should disregard caliber. You’ll never develop any reckless tendency if you train yourself to treat them as if they were all lasers, be they 22lr or 7 mm RUMs.
So, no wrong answer. This is an individual thing where personal preference and availability rule the topic. And where pelts aren't an issue (for most people they aren’t) I credit the big guns for being humane. We all pull shots. Anyone who claims they don’t is ******* away their credibility. A hit pulled behind the diaphragm with a 270 has a very different result than a foul hit with a 17. Those regrettable scenarios always favor the bigger guns.
If I had to sell everything off, I’d keep the one I almost never use now and I’d be back with my 243. If it happened to be a 270, so be it. That would be my “varmint gun” and I’d shoot it happily because of everything it has going for it. Bonus that some little critter varminting will keep me super tuned with that rig, over-kill or not.
So, is your 270 a rig for little vermin? In the words of Napoleon Dynamite, “Heck, yeah!”