The SB16-Ultra is very powerful for a sealed sub of its size, but it isn't going to outperform two R-115SW subs. Its real advantage is the deep bass extension for a sealed sub. It's one of the few sealed subs that does reasonably well in deep bass. But it still probably doesn't have a headroom advantage over a R-115SW at the port tuning. Whats more is how inefficient it is. It needs a lot more power than most subs to achieve the same SPLs. If I were you I would be looking at dual ported subs. I would be looking dual PB-3000s, dual Paradigm Defiance X15s, dual Hsu VTF-3 mk5s or VTF15h mk2s, Outlaw Audio Ultra-X13s, Monoprice 15" Ultras. Two of any of those will give you an upgrade in headroom, linearity, and extension.