I was calling the OP confused - my bad. I did not see he was saying RIVA.
This here says Ego is 3.4 volts as have many people on this forum
"The battery of the basic version is 650 mAh – significantly greater than any skinny e-cig battery (even the XLs and Megas) … and it is greater than the wimpier mods at 340 mAh (they look neat with all those lights, but at ~$100?). The voltage, however, is only 3.4V: slightly more than the 3.2V Joye 510, but less than the 801, 901, or especially the 3.7V Kr8."
Egos and Rivas, Hellos, Oh My! | Vaping Guides
I cannot answer the vapor thing other than 510+Boge soft cap standard resistance carto seems to make more vapor than KR8 with a vapor4life wow carto. If I put a Boge carto on the KR8 and use the same exact juice, maybe it will make the same vapor or more. But those V4L WOW cartos are wound very tight and the Coolcarts don't give me much more vapor than the WOW carts. Maybe the Boge blanks are the key to better vapor. I don't know yet.
I would consider a 510 a sideways step from KR808D-1. A 510 also has less battery charge than a standard KR8 - you need 510 mega xl batteries to be the same charge as KR8 standard. The best thing about the 510 IMO is the totally sealed end on the manual batteries and the upgrade path to Ego/Riva 510. I enjoy vaping both 510 and KR8.
I think an upgrade would be to Ego or Riva or anything else that can use all of the LR attys and cartos. If you want higher voltage than 3.4 (Ego) or 3.7 (KR8) then you need to go to 5-volt mods which I don't know anything about. But you can get a similar effect by using LR atomizers and cartos on an Ego or Riva (or KR8 fat battery versions PigCig or Elegant Easy). Less resistance attys/cartos on same battery voltage = hotter hit. With high voltage devices you can pop LR stuff so you use standard resistance stuff on higher voltage = hotter hit.