If you're sticking to cartos, I wouldn't recommend more than 15W. Cartos can't wick juice to the coils fast enough for high power builds and so that's where you get a burning flavor. Plus pushing too much power through a carto that isn't being cooled by the e-liquid fast enough will result in burned out cartos really quick.
If you want to run more power, RDAs are the way to go. You're really only limited by how effective your wicks are. And if you bust a coil from heat (which is unlikely), you can build another one for a few cents worth of wire and like 10 minutes of your time.
I currently push about 45W on my current set up, but I've gone as high as 60W without a burning taste. This is with an RDA, parallel coils, and lots of cotton.
Of course, once you get to these high power setups, e-liquid consumption will go through the roof. Space Jam juice isn't cheap, and I could go through 30ml of liquid every 4 days if I'm not watching my consumption.