The Velox can be flown with either the DLE20 or 30. From what I've heard 3DHS is doing a redesign on the Velox and it will be returning this year. The Slick 72" will need a 30cc due to the extra weight. The 20cc size is a tough one for 3D, kind of hard to find one, I'd say stay around 8-9 lbs rtf and you will be ok on power. That said there are several 3D profiles that folks are putting 20cc on if you want to consider those. Let us know what you decide on. DG