I think the "maximum spl" thing is being misinterpreted here. That's not an exact spec as to how loud the driver will get, it's a representation of how efficient the subwoofer will be in said enclosure. It's very well possible that the pioneer would be more efficient in the enclosure for many reasons:
1. It requires a smaller box, both sealed and ported. The larger the box is, the more efficient the sub will be. Here's a hypothetical situation to help explain....Let's say that you have two drivers (sub Y and sub Z). Y requires a min. of 2 cubes ported, whereas sub Z requires 3 cubes. Sub Y will be more efficient in three cubes than sub Z would be because it would be like putting sub Z in a 4 cube box (well....not exactly, but you get the idea). EFFICIENCY DOESN'T ALWAYS MEAN LOUDNESS. Yes, it plays a part of it, but there are many other factors that come into play.
2. The RE HC is more of an SPL-oriented driver than the Pioneer. Without knowing the exact specs for either driver, I'm willing to bet that the Pioneer is a more efficient driver in the first place. If high efficiency directly translated into sound pressure, we'd all be competing with Kappa Perfects and MB Quarts //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
3. WinISD will NOT tell you how loud a sub will be in a given box....hell....it's not even good at close estimates. It gives you an idealized version of how it SHOULD perform in a given enclosure. I only use it to tweak boxes once I already have a design laid out.