One of the guys I hunt with uses a 270 and has taken more elk with one shot than a lot ever will. Not that the gun is the real reason as he is very good and has some lady luck with picking his spots, but using a 270 with 150 gr nosler part hasn't caused him any concern. Personally I have taken 2 elk and 3 moose with a 270 using either 140 gr failsafes or 150 gr nosler parts, needing only one shot on all occasions. I believe first and foremost you must select a solid constructed and premium bullet when chasing the bigger critters like moose and elk. Secondly one must know his/her limitations both ability and gun wise, you must also be able to stick to those in the heat of the moment. While a larger gun may buy you more range and a few different angles, one still owes it to the animals to pick a shot that presents the best outcome..to me their is no such thing as grey areas when it comes to shooting, either you have the shot or you don't(forcing the issue can and will only result in let downs over time). If you expect shots to be outside those limitations than taking the 270 may not be the best option. For example; when I used a 270 for bigger game I limited myself to 250 max and preferably under 200 and a good view of the H/L region, which never presented me with any problems in my areas. My suggestion would find out from others what type of range the shots typically will be and if that fits into your limitations. If so then you can choose either option stick with the 270 you know or opt for a new gun for this hunt. Of course going bigger never hurts, so if you think you'll hunt elk or require a larger rifle in the future that isn't a bad choice either...just buy it and hit the range hard to get familar to the new toy so that come time for the trip you have confidence and know what you can and can't do! I still suggest a premium bullet like mentioned in other posts for elk.

Best of luck and enjoy!