I'd go hybrid for simplicity. Factory overclocks aren't indicative of actual GPU boost clocks.
Lower temps equal higher boost clock so you definitely want water cooling.
Kingpin isn't worth it for normal or non ln2 uses. The extra stuff just won't benefit folding and gaming. It's just targeted at ln2 benchmark use.
Just my 2 cents.

Hybrid if you are only going one card.  If you get the real folding bug and start adding cards then you need to look at air cooling which is what I do or custom loop for cooling.  I change cards to often for me to mess with loops.

My current setup is a folding rack, with motherboard sitting horizontal, and cards vertical.
I currently have a 120mm fan (I believe) that fits perfectly under 2 card's front metal lip, and the rack, pulling the hot air between 2 cards out.
It is very similar to the hybrid card's external fan in size.
 
There are still more questions.
1- How long are the flexible hoses?
In my case, I will have to move the external fan past the metal piece, that usually mounts on the case.
That way I could use the fan, to suck out the air between 2 cards (currently my top card is a blower type 2080, and my bottom card an open type 2080. The open 2080 I might replace with a hybrid or open type card 2080 ti).
So the hoses need to be long enough to have the fan reach this far.
Using an open type, air cooled, won't be a problem, as the bottom card is close to the PSU fan, which sucks out the air from the card, through the PSU unit, exiting the rack.
2- Is this a closed circuit?
If not, the liquid will surely evaporate over time.
If it is, it might be hard to replenish the liquid.
I don't see any sort of buffering device, that will catch bubbles or air.
3- What is the power consumption of the cooling circuit?
for occasional cooling a few watts won't matter much, but even 10Watts more power draw, 24/7 can result in $15 a year higher overall cost. So anything costing me more electricity, won't be very beneficial, unless it really comes with a speed bump.
Speed bumps on cards are set between 50-60C, 60-70C, 70-80C, and above 83C. 
So if my card, aircooled would run at 79C, and water cooled it runs at 71C, I won't see any performance boost at all.
If the air cooled card runs at 71C, and the water cooled card runs at 69C, it might jump to the next GPU boost speed level. Then again, this level is easily attained by overclocking the card to the same speeds.
I suspect the card has a pump that will keep the fluid in motion, as I don't believe for such a small unit convection will work well.
So when it gets more than a few watts of difference on the cooling circuit, I might pass on the hybrid card.
4- I'm also concerned about the hose lifetime, operating at high temperatures for prolonged amounts of time, in a chemical... I'm sure even the best rubber will rot over time, and start leaking.
Since this is a server that is mostly unattended, leaking hoses could be disastrous (only noticed perhaps hours or days later).
5- Despite all this, the hybrid card in a way, still is aircooled. Instead of a fan blowing directly on a cooling circuit, now the cooling circuit is separate from the card, but a similar aircooling is going on.
I wonder if it's really that much better?
 
To me it still sounds like the air cooling is the better choice.

I have yet to run into issues with the host length on my aio units. I have 2 hybrids in each rig and while taught, none they are installed at the top of the case on 1 rig and on the other 1 is taking up the rear exhaust slot as 3 roads wouldn't fit across the top of the case (CPU aio).
They are of course the next best thing to 24/7 and the extended warranty covers the water parts as well.