I'm trying to use WinISD backwards, as I've already glassed a custom, irregularly-shaped sub box and am now trying to find the proper woofer. The box is long and narrow and about .5 ft^3, with only enough room for an 8" sub. Sub will be driven by 2 channels mono-bridged from a Cadence Q400, giving 200W RMS at 4 ohms.
Here is my transfer function magnitude graph, which I think would point towards the RE8. However, I don't trust the numbers I've input into the driver file for the RE8, since the calculated Vas came out to be about half of what RE claims it should be.

My other problem is cone excursion. The RE8 Xmax is 12mm and the eD9Kv.2 is 14.1mm, which don't work, and the ID8 D4 V.3 is 15mm which is OK. My amp does not have a sub-sonic filter that I could find.

So my questions are:
1. Does anyone have a .wpr file for a Resonant RE8 that I could double check against?
2. Should I just go with the Image Dynamics ID8 V.3, since it seems safest from a cone excursion standpoint?
3. If I wire a 4 ohm 2DVC in series to give an 8 ohm load, does that change the power output to the sub?
4. This may be dangerous to ask, but are there any other 8" subs to look at? I tried a couple JL Audios, which gave nice transfer function graphs but only have 7.6mm Xmax, which isn't close.
Thanks