With my skater dreams crushed by the current insurance market, I have moved my sites to a sit down v-bottom. I really like the 38 donzi zrc. The fountains are cool, but they only have 4 seats. Does anybody else make a sit down v-bottom.

note: I am not buying a new boat, I would like a several year old used one.

Outerlimits GTX for a used boat is the way to go.

Cig Gladiator.....

Donzi 38 ZR Comp I am pretty sure is a sit down boat.

I have a nasty gladiator Ill sell staggered 750 zuls

Red buds glad is a great deal now at 114, and its at loto. its a great ride, ive been in it and throttle it. very fun

Laveycraft 39 EVO

Don't know your price rang but the 42 Statement is the best sit down
V bottom out on the water.

Here's a few Skater sit down Vee's. One new One used for sale.

38 Donzi Competition hands down!
Best sit down V out there. It rides like a Cadillac, handles like it is on rails and has proven its worth with multiple National and World Championships.
Before I bought mine, I test rode the Donzi, Gladiator, and an Outerlimits 37 GTX. The Donzi was the clear choice for me. I like the older Outerlimits GTXs but finding a good one at a good price is tough. I love the look of the Gladiators but wasn't sold on it and the back seat is a rough ride with very little freeboard. The Fountain as you said has a very tight cockpit.
Now if you have deeper pockets, the newer epoxy Outerlimits, Statement and Skater V's are really nice.
Will an epoxy boat outrun the Zr hp for hp......yes.
Will an epoxy boat cost twice as much ... yes.
Personally, I am not a fan of the ride in an epoxy boat. Every ripple and bump can be felt because the boat is so rigid.
In the end it will be up to you but I HIGHLY recommend getting in a few different ones to see what is best for you!