Theres the Vapestack at Madvapes.Ive heard good things.
The VapeStack is only 3.7 volts right now, it will likely have a 6 volt cup available soon, and hopefully a 5 volt arrangement sometime in the future.
I've been vaping 5 volts for a long time - I primarily used Cartomizers at 5 volts on a Prodigy V1 and on a V4L pass thru. I bought the VapeStack because it is so nice in design (button on top, light aluminum body) and it is the smallest mod I've seen. Shorter and wider than the GG Slim for example. I use a 510 on it sometimes, but mostly I use the new Premium cartomizers and I get plenty of vapor with those at 3.7 volts. I even ended up selling my Prodigy because of it. 3.7 is great with the new premium cartos. 3.7 would be too little with regular cartos or with 901 atties.
The cheapest way to experience 5 volts is a $15 pass thru. Then you can see if you think it is worth a large mod for 5 volts or if you'd rather have a small mod and use Premium cartos or Low Resistance atties to simulate 5 volts.
I generally find 6 volts plus to be too hot and kill atties too fast - so I would definitely be deciding between 5 volts and/or Premium/LR atties. Atties designed for high voltage are more expensive and too often out of stock - higher than 5 volts is not worth the trouble.