Yes i can tell a difference. I did a bucket test with the 4, and then with the 5.5… if i remember correctly, it was like a 10-15 second difference. When rinsing with the ball valve, i can feel the increased force of it over the 4. I also use an injector bypass, and it makes a noticeable difference when i bypass the injector.
As far as the 2400 PSI (which with 200 feet of hose, it’s probably closer to 2000… one of these days i will check), i haven’t had any issues. I just cleaned 40k square foot parking lot with the 5.5, a 19" SC, and cold water only. Granted, the parking lot had very little oil, but it did have heavy organic staining. Here’s a picture of it partway through the cleaning:
It cleaned up nicely, but I did have some faint striping over most of the concrete. Not sure if that was due to the low PSI, and/or lack of hot water, or if the striping would have occurred even with more PSI and heat. Here you can see the striping, except for in the second parking spot… that spot i had post treated with straight bleach in a pump up to test if it would remove the striping, and it did. I ended up X-Jetting 10% straight for the rest, and it took care of most of the stripes, except for a few spots here and there that i used a pump up on. I had pretreated by downstreaming straight 10% bleach, with a little EBC mixed in. A stronger pretreat may have helped with the striping also, i suppose.