I'm pretty new to the site, so I wasn't FULLY aware of the no VS threads, but I can understand it, I've seen many get ugly real fast, not just on car audio forums, but any forum.
I've unfortunately only seen/heard one sundown in my life and it was an 8" SA series. It was a wickedly loud little beast and seemed to retain much clarity if I recall, but it's been 4-5 years since I heard it, many subs have been heard since.
Alpine on the other hand I've heard numerous Type-R setups, just none of their current 1k line.
"I" wouldn't push my luck on seeing ow long the Sundowns take 2K, I can't help but believe their life would be dramatically shortened if fed such regularly. Granted, if the gain were set for 2K with the amp, chances are rare the subs would ever see the full 2K and even if they did, it's be quite rare. Alpine's Type-Rs have earned a similar rep for taking abuse and I've known many to last quite a while under such conditions.
Alpine is mainstream, while Sundown isn't so much. Chances are there's a larger following for Sundown on Audio forums such as this, but again, that's getting into hot water.
May want to use WinISD and plot both of the subs. It's not a clear indication on which will be louder, but it can give you insight into which is likely to be louder.
Both are sure to be more than capable of playing loud enough to cause permanent hearing damage/loss and get you sound ordinance violations, so...
As said though, a large factor is going to be the enclosure used. Just how much room have you for the enclosure? Loud deep lows tends to take large ported enclosures tuned low.
Oh, and your amplifier doesn't have two channels, it's a mono amplifier with two sets of speaker terminals wire in parallel internally. Wiring as you say, you will have each sub wired with it's coils in series for a 4 ohm load and with both wired to the amplifier, it's see a 2 ohm load and be capable of producing around 1600RMS. That's fine for the Sundown subs, but for the Alpines rated at 1K each, you'd want to opt for the DVC 4 ohm models and wire them in parallel/parallel for a 1 ohm final impedance.
And then since you have said the money isn't an issue, perhaps you can somehow find a way to swing for a "better" amplifier, perhaps something like a Soundqubed Q1-2200D which is sure to produce every bit of 2k and then some.