megaraid_sas (H710), fast SSD's, poor RAID0 performance

Hello there, I have a server in our test lab (specs below) that doesn't appear to be getting nearly the write speeds that I was expecting (test details below). In "top" terminology, there is one CPU core at about 30% SI and each core shows anywhere from 1 to 15 % SY and about the same for WA.

My main question: what tools do I need to get some visibility as to what is going on within the megaraid_sas module and on the SAS controller itself? I have gone about as far as I can go with utilities such as top and MegaCli.

For simplicity, I am only focusing on raw write speed straight to the block device. I have a few benchmarks I use, mainly Orion and some of the Phoronix suite, but Currently the easiest test is just:

dd if=/dev/zero of=/dev/sdc ibs=1048576 obs=1048576

The main symptom is that with a single disk I can push > 300MB/sec, and with a pair in RAID0 I can get over 600MB/sec, but with 5 of these in RAID0 it never goes above around 700MB/sec. My next test will be to use each disk as a separate device and try software raid (or just writing to each disk simultaneously).

Thanks,
Mark

p.s. system specs:

Dell 720xd, H710 ("mini") controller
5x Micron P300 SATA SLC SSD's