Center of chest shots, rear quartering shots, front quartering shots, they all work flawlessly for me using a .243 or .25-06 using any decent bullet from the Sierra GK to the Barnes TTSX. Although I'd rather have a Barnes up the snout if I know I might take any shot presented on a large buck. I don't pass just because the deer isn't perfectly perpendicular to me when it's time to shoot. BTDT several times.
I've seen too many X/TSX/TTSX bullets plow though 3' of game from .243 and .25-06 rifles, creating plenty or damage along the way, to support the notion that only the most ideal shots can be taken when using those cartridges.
I've watched my girls shoot deer with their 243 and 85gr TSX. Works quite well. However, we could not find the one deer before dark (I thought it was going to tip over, but it made it to the big timber and we could not get another shot in it). We found it the next day dead, but the coyotes had been at it. The shot was a little low, but still in the vitals.
I have used a 25-06 extensively for 30 years. It is MY minimum. I always used 115-120 gr bullets like the Speer GS or Barnes TSX. IMO, it is a significant step up from the 243 and little separates it from a 270 130gr bullet. Just my opinion.
Now if I was spending big money on a possibly once in a lifetime trip to AB or SASK for BIG deer, I'd bring my 280, 7mag, 30-06, 300 whatever. I'd use a premium bullet so that I'd be able to ensure good penetration even from an extreme quartering shot. You'll be good to show if you can shoot. Shots can be from 20-450yds quite easily in Western Canada.
Be prepared for shooting in extreme cold also. If you have your glove off for a lengthy period of time, it can be hard to squeeze the trigger. BTDT.
