This has probably been answered, I'm posting because my guppy brain will forget what I was going to say after I read a couple of more pages.
The "Mega" cartos from IKV are what he calls XLs. They are just regular 45mm 510s. I wasn't blown away by IKV. I like the Platinum, but they don't have a flange, which I find a hassle. The Mega Fusions (510) have a flange, but the filler is different than Smoktechs (Boges are different too). They seem to dry out faster to me. I have a couple more boxes, so I'm sure I'll give them another shot, but I wasn't impressed enough to keep checking the IKV website all the time to see if there is stock.
For dripping and my bottom-feeders, I use Joyetech LR 306s (1.5Ω) that I buy in bulk from Vapor Kings. I have some Joyetech 510s, but I think the resistance is 2.0 or 2.2, whichever it is it's to cool for my BFs. Lately, I've been using hybrids from Vapage, but they only fit in bottom-feeders.They are technically 510, but there is something different with the connector pin and they won't screw onto anything else.