Is Volvo making the DPX again?
You can not compare a Volvo DPX to a Merc BIII; Vary different animals.
I have a bud with a 275HP Volvo DP in/on a 18' Donzi. That boat runs great and tops out around 65mph.

No, unfortunately they're not making it again. And you're right you cannot compare it to a B3.

A friend has a U19 with a 275 running through a Duoprop that runs 68 mph with modified F9s.

They do not make the DPX anymore however the currently produced DPS is very similar. Definitely prettier. Improved in some ways and maybe not quite as strong in others. Still has the integral hyd. steering.

Arguably still better than a standard Merc Bravo. As with anything, it is going to depend on the HP in front of it, as well as the way you drive it.

The DPS does not have the external steering. However they make a DPR duoprop drive that is made for high speed Diesel applications with external steering!

I thought the DPX was thew hot setup for the single V bat boat racing class a few years back with stock speeds in the 70 - 80 range. What are the Bat boats using now?

I've been hearing nothing but good things about the drives.....didn't know anything about them. I am leaning towards putting it on the boat. Does anyone know whether the cut outs are similar on the transom? Would I be able to go back to a Bravo if it doesn't work out without having to fill in the transom?

I don't know about the cut-outs but I know Donzi used the same X as the Bravo.

Yes the Bat Boats did use the DPX. I don't know what they are using now.

The cutouts are not the same. The Volvos have a larger cutout area. There was, and I believe, still available aluminum adapter plates to go from Volvo to Merc drives. The other possibility might be to cheat the cutout to a size small enough to still accomadate a Bravo. It looks like on mine the cutout could be kept smaller without much consequence based on what I can see. Its tight with those twin 540s in there

My Donzi Classic has a Volvo 7.4gsi/DPX package. Strong out the hole, very good mid-range pull, and 72 mph wot...with hands-free "on rails" handling! E-4 props, zero problems, very sweet set-up.