If you have a true 3.7v device, I'd suggest trying an LR atty first. The difference between that configuration and a 5v device with a regular atty is negligible.
High voltage vaping is a misleading term. The combination of the voltage and the resistance of the atomizer determine the wattage being used. The formula to calculate wattage is Voltage squared / Resistance. A 3.7v device with a 1.5 ohm LR atty runs at 9.1 watts. A 5v device with a 2.5 ohm atty runs at 10 watts.
Yes, the ego and the riva both use 510 attys, though neither are 5v devices.