650hp hands down . I’ve looked at both. The 870 is pretty good but there are a few out there with problems . In my research the Prochem 650 had way less problems. Plus I’ve heard rumors that they are doing away with the 870
Only person that can answer this is you. How do you honestly see your work load? Can you run it hard with 2 wands on every job and carry 200-400 gallons of fresh water to each job? Then a 875 since it will burn and divert a lot of water. If your a 1-2 wand guy then I️ would do a 650. Price out your van, machine and all the extra and see where your at $$ wise. Not much more you could do a Aerotech from my understanding if you can keep it busy.
650 got 4 of them. Only drawback is need to watch belt tension. We usually tighten every 75-100 hours. Only takes about 20 min. Plenty of vacuum with the series 6 blower. Plenty of heat will stay buried at 260 degrees at the machine. Motor is bulletproof
so ive never worked with a 870, but ran two trucks with 650s and they are beasts, dual wanded all the time and never had a issue with suction or heat, ran out 500 ft and had plenty of suction. maintenance wise they have allot of electronics but we never had any issues other than loosing one heat exchanger and had to have it replaced... last time i worked for them both machines had over 3000 hrs. To work with them i loved them. And speaking as an mechanical designer of heavy machinery for 20 years they are great machines, i would buy one in a heartbeat if i had the money... but my legend will have to do for now