First - you definitely have tried what most people like which is 2 ohm Boge cartos used with suitable
juice (by suitable I mean thin - I use PG w/ 20% or less VG)?
The Riva 510 kits at Liberty-Flights.com are all the new 3.7v models from the correct manufacturer so that would be a bit of a heat upgrade. (Ego is 3.4v). These are the same heat as all of the 3.7v mods. The loose batteries may or may not be 3.7v but the Riva 510 SE loose batteries are 3.7v.
So 3.7v Riva 510 or and 3.7v mods would be a slight step up in heat for all of you current attys and cartos. Mods have choices like box mods, tube mods, bottom feeders.
Beyond that is variable voltage
Most tanks are for 3.7v batteries
Ecig Mods Database on the Browse by Features page
http://www.ecigarette-mods.com/info/browse-by-features/
If you look at Juice Feeders, that section includes some of the juice tank attachments. There are many more too. Some tanks use CE2 guts, some hold an entire punched carto. And look at the rest of the database to see mods.