Believe me, I've already thought about it as well as others. If I use KR8's on 3 volts though, I can use what I already have. I've just been hoping for 510's at 3Ω, but it doesn't look like that will happen.
Br, they have a menu drop-down from which to choose when you buy the 510 XL
Yes, one of them is 3.0 to 3.2 ohms:
http://www.e-liquid.cn/catalog/product_info.php?cPath=113&products_id=296
It's been there for a while now