I have one on my 98 EFI. It is supposed to make 132 hp with a single pipe. I really like it and have not had any problems yet. I have put 2500 miles on it since I bought it 1 1/2 years ago. Try to find a used one. Make sure you clutch it accordingly.
I have around 1500 miles on my 711, bought it used last year. I average around 12mpg with it and it is a strong runner from engagement through top end. Seems very reliable so far. I am still dialing in the clutches. But I really like it over the performance of the stock 600.
I have a Black Magic 711 Invader in my 01 Sno-Pro chassis. I guess I probably have around 400 miles on it since I got it. Trail converted from a full race motor. Very strong, and seems to be pretty reliable so far. Change jets accordingly, but a dial-a-jet or ATACC would fix that. Certainly is fun to ride. Passes everything except a the gas station. If your looking for something to just pull the rope and go, I'd recommend a 800 or 900 instead.
The D&D kit uses your stock head (with combustion chambers machined by D&D) but the jugs have "PREDATOR 700" cast on their side. You could file the lettering down I am sure, and clean everything up and nobody would know, but not that many people look at the side of your cylinders anyway. You have to either use the D&D single or twins with their 711 kit - EFI can only use the single.