I’m getting an AC so i’m kinda curious about this. What’s the difference in term of feel and playability? Which plays better in your opinion? 
I have tried a 67.5g one and loved it.It played amazingly well. Will be curious to see how different a 66.5 one plays.
I love lighter throws, but that’s just my preference. You’d have to try a few throws with different weights, then decide what you like. It’s all preference. What I like could be different from what someone else likes.
I’d love to try ANY two yoyos that are otherwise “the same” but for a 1g weight difference and really appreciate what kind of difference 1g can make. In this case, it’s 1.5%, which is probably enough to notice, though I think the difference doesn’t suddenly make one a “lighter” throw. 66.5g is still considered pretty middle in terms of weight.
The lighter one feels way better. The heavy one felt like a rock tied to a string.
To me in doesnt feel like a rock. I just bought a heavy run ac a couple month ago new on yye cuz one day i checked and its was there, just one latitude 53 siting there so i got it. To me it fells powerful i really think the weight kicks up the sleep time a bit. Still floaty but not like a chief
I find that the lighter run of any CLYW throw seems to play noticeably faster. I prefer lighter throws 