Depends.... If the load is light two controller will produce higher throughput. If the load is medium -high then two controller would increase the CPU/IRQ load thus lowering the overall server performance,  NIC interface throughput would also decrease. Then you need to consider, with two controllers, if functions such as temp files, db temp files, pagefile are placing  traffic between the controllers, this would take up  bus bandwith , not normally placed on the bus by a single controller. Then consider bus saturation. If you have SAS 6.0 drives your not going to saturate the H700, if it were an old/low end controller (SAS 3.0) you would saturate the controller, then a second controller would be called for. For maximum proformance, you would want to use an SSD raid1, (for safety, with a hotspare or at least a cold spare on hand ) for at least the tempDBs, transaction logs, tempfiles, pagefile, logs, and for good measure the OS. Under ANY circumstances the OS should be separated from the data, at minimum a separate partition, at best on a separate spindle set from the data . To complicate your question, a couple SSDs added to the controller could saturate it, but I doubt the SSDs with the setup as above would   Saturation.... www.dell.com/.../perc-technical-guidebook.pdf In small disk drive configurations (one to eight drives) the aggregate media rate of the disks (the speed at which the disk heads can read and write data) become the bottleneck for storage throughput. As business storage needs grow, IT centers can add more disk drives to their storage infrastructure, and the latest generation of SAS allows server performance to scale past the 3Gb/s SAS performance limitations: from 2.4 GB/s to 4.8 GB/s unidirectional. Table 3. SAS Performance Details SAS Generation PCI-Express Interface Approximate number of SAS HDDs required saturate bandwidth (RAID 0) 1.0 (3Gb) 1.0 8 to10 2.0 (6Gb) 2.0 16 to 20 Saturation..... serverfault.com/.../how-many-disks-can-saturate-a-6gsas-controller-lsi-9260-8i   Benchmarks, some Dutch, benchmark in English, many of the benchmarks are for SSD and SATA, if you dig there are SAS benchmarks..... tweakers.net/.../13
On a PowerEdge R910 configured with the 16 internal disk backplane, is it possible to manage / configure select groups of disks with individual H700 controllers?  Would there be a performance benefit to running the OS (Windows) via integrated RAID and use a separate H700 for two other Raid1 containers, and another H700 for a Raid 5 container?
Disk Management on PowerEdge R910