25w on a single coil in a subtank RBA is about right, if you want to get more power and heat in try doing a twisted pair single coil, just take a single length of Kanthal or whatever wire you use, i recommend 26awg, take the two ends and join them together with a hard twist, then get two pens/pencils, put one each into the looped end and twisted end, hold one end tighter and the pull on the other and start to twist...
If you have a drill its easier, you can trap both ends in the chuck...
Just twist until tightly would together, i actually use the CoilMaster Coiler and a Kuro coil to make mine, this will give you thicker wire and thus require more power, wrap around a 2.5mm bit, space each wrap slightly so they are not touching, then fit to the deck and pulse to check there are not hot spots, strum if needs be.
Now for the Rayon wick, get a piece just over an inch long, reduce it to 1.5 times the diameter of your coil diameter, then tightly twist one end and feed through the coil, once you get the twisted piece of rayon through and hit the untwisted rayon it should be tightish going through the coil, just a little resistance, pull till you have a goo fluffy amount each side of the coil and then pull back and forth to settle it in.
Now cut the tails so there is just enough to touch the deck on either side and no more, this is where i tend to pinch the ends and then trim a little off, then fluff it up and push onto teh deck, you can add a little juice to help make it stay in place, than attach the chimney and tank and fill, let it site for 5 minutes to really wick, set you mod to 20-25w and take a few toots, then increase the power 5w at a time and see how it goes..