UPDATE and SOLUTION: After a few days of wondering what's going on and subsequently posting my question to the community, I found the problem. To make room for other cards, I moved the PERC H730 from the full length PCIe slot in position 4 to the top slot in position 1. I didn't realize those slots changed bandwidth quite that drastically. After moving the PERC H730 back to PCIe slot 4, I'm getting 4000 MB/s read and 3700 MB/s write which is what I'd expect for 8x 500MB/s drives in a RAID 0. The PCIe slot the RAID controller was in was the bottleneck.
I have a PowerEdge T430 with 8x Samsung 830 DCT 960GB on a Perc H700 controller and Windows Server 2016 Datacenter in a RAID 0 setup (this is for testing).The single drives are 500+ MB/s read and write on the PERC H700 as a non-RAID disk. 6 of them in RAID 0 was capped at ~1600 MB/s Read/Write. Adding 2 more drives to the RAID 0 produced no increase in speed. So 8 drive RAID 0 is also ~1600 MB/s. That doesn't seem right to me as I'd expect to increase speed as I add drives. The initial speed of 1600 for 6 drives seems around half of what it should be (shouldn't 6x 500MB/s drives be around 3k MB/s?) I'm not sure where the bottleneck is. Any insight is appreciated.
T430 with 8x Samsung DCT SSDs on PERC H730 Capped IO Speeds