According to my balistic calculator a 6.5cm with 140gr SMK at 500 yards with a 10mph cross wind at 90 degrees needs 3.3moa correction. 308 win with 168gr BTHP at 500 yards with 10mph cross wind at 90 degrees needs 4moa of correction.
Is 0.7moa really that much difference at 500 yards? You can reduce the 308 wind drift going with heavier/lower BC projectiles. Especially when a 168gr is just mid weight for a 308 and one could easily shoot a 175-190gr to buck the wind better.
I love my 6.5's and think it's a great cartridge but inside 600 yards there is nothing I can do with it that someone at the table beside me couldn't do with a 308 with a couple more clicks of correction.
If a guy was starting out and didn't already have a 308 I say go for the 6.5 but if someone is already shooting a quality 308 it's not worth changing over unless 800+ yards was on the menu on a regular basis. Or if someone was competing and first shot hits got you more points sure.
But for the average guy going to the range who's bored at 100 yards and wants to try shooting 500 yards it is not going to make much difference other than 6.5 is less common in stores than 308, and 308 has a lot more factory options for ammo if you're not a handloader (I know, we're in the reloading section so chances are good we all reload).
Only other reason I would suggest a switch is if someone was a little sensitive to recoil, the 6.5 has noticeably less recoil.
I do support guys buying a 6.5cm but they should do it for the right reasons, not because some guys said it's more accurate. It is not more accurate, it's faster and flatter so it requires less correction, it also maintains supersonic further which is good if 1000+ yards is your goal. But inside 800 yards it's not a big deal. How many guys even have a place to shoot past 800 yards? Around here most ranges are only 300 yards so unless you own land or know a good spot a 6.5 is just something different, not really something better.
If you're a hunter the 308 is also a better choice, better selection of projectiles to suit hunting different animals over different terrain.