I can only get 900 or so psi out of my cds. I usually clean at 700 psi. As long as you compensate with more scrubbing and chemicals you can clean anything out there that's cleanable. I wouldn't say just 90%. In other words it will take you longer but nothing is out of reach with lower pressure. That's my opinion for what it's worth. Remember tact.
You can overdo it. If I go 1200 PSI on a poorly installed grout line with the turbo, I’ll see some damage. You’ll know far to push you luck after you clean a couple of bad installs.