As with all hunting, shot placement is (almost) everything. So long as your bullet has enough down range energy and appropriate construction.
I don't advocate trying to emulate shots such as that shown in the video below (long-range, VLD bullets etc... whole different can of worms) but it shows that a .243Win
can do the job so long as you can:
[youtube]
http://youtu.be/hY0w1c-gf18[/youtube]
That said, I have shot a fallow buck, high-heart, at around 110yds with a 100gr SP bullet and he didn't even flinch. I thought I'd missed as he ambled slowly toward me, though he seemed a little sluggish. Since the range had closed down I decided to take a second shot in case he was injured. He dropped to a neck shot. At the gralloch, I found the first shot was a perfect placement, destroying the atria of the heart. The bullet hadn't exited.
I since switched to 95gr SST and haven't had any similar experiences but I now favour a larger calibre if I'm hunting larger deer species.
The .243Win is a good (and versatile) clambering but not my first choice for deer. I only got one because, at the time, I had a closed FAC and the land inspection stated: "can use your .308 from high-seats but would need .243 on foot." Go figure!
Gave me an excuse to get a heavy-barrelled .243 which I set-up for "tactical" comps and foxing (plus opportunistic deer since I still use the 95gr SST).
Good overview, which you've probably read,
HERE
The .243 also offers lots of potential for future rebarreling.
Every cloud has a silver-lining, as they say.