A few preliminary PC Vantage HDD Suite results:

32K strip, NRA, DCD, DIO:

6+1R5, WT: 20129
8R0, WT: 27510
6+1R5, WB: 57490
8R0, WB: 67234

So, the scores more than double with WB enabled (almost triple with the R5 setup), in spite of the big decline in 4K random reads. I'm happy again now that I got the BBUs for the RAID cards.

I solved my overheating PWM problem by moving the fan I had blowing on the RAID cards on top of the CPU heatsink, blowing down toward the motherboard. It's a tight fit, and a bit of a hack, but it seems to work, based on a short Linx run. I'll do a full run soon to make sure (takes ages using the "All" setting with 24GB of RAM).

First, though, I noticed that the 14cm fan in the top of the PC-P80 is blowing into the case, instead of exhausting. In addition to being a pretty obvious thing, the description on their web site even says it should be an exhaust fan (hot air rises and all that)--so I'm going to try to flip it over to get it flowing in the right direction.

Temporarily, I put the factory fan back on the 5-drive HDD cage. It sucks air through the cage and exhausts it toward the RAID cards, but not with as much volume as I'd like, and it's also too damn loud. I'll have to find or buy a replacement.