Ok so it seems that I do read too much review !! I was just worried that the bottom-oriented fan of the PSU had not enough space in the bottom to get its air. It seems that you make it work succesfully anyway.
For the middle fan, I think the Off-Low-Med-High setting would depend on the required operating temperature of the HD.
I have two WD 5000KS (well, had, one seems to have died, but that is not the point) running in the lower chamber, together with a Corsair HX620, and when running the fan at the low setting my hard drives are reported as 37 degrees celcius, SpeedFan online information tolds me 39 is average for this drive. So in short: even at low fan setting it's cooler then the average drive
And blocking the grill around the PSU sounds like a good idea as well, making more air go through it.