The $60 CDM walbro knockoff 255 that we have been testing for the last year seems to be working well... So far it has run from -53C (-63F) to +33C (91F), and has about 50,000km (~31,000miles) in an oilfield application. So it sees lots of idling time, as well as highway, stop and go city, gravel road, and off road. Snow, salt, water, ect...
It is only on about a 450whp truck, but I would suspect it would fuel up to about 600hp, after that just add a second one in parallel...
Obviously it is externally regulated, by another off brand regulator that we found at the local speed shop for cheap.
I'm not saying this is the solution for everyone, but for our work truck, it is cheaper to keep a spare new one in a box, with a couple extra hose clamps, then it is to even try one of these other systems.