what contour? now days i have been leaning towards the shorter, stiffer barrels. less harmonics and vibration. i know that with a shorter barrel one is sacrificing velocity but some cartridges don't gain much, if anything with excessive barrel lengths.
Velocity vs. accuracy ..... there is definitely a fine line there to figure out. personal preference is what is comes down to.
IMHO with the .243 I think you could probably make do with a 23" to 25". with some of the newer powders you should be able to make some good speed outta the 24".
i got a .300 WSM
with a 23" barrel and got the berger 190 vlds running at 3050 fps. RL-17 powder and shooting .248 3 shot groups.