There are quite many ways to increase PC hardware performance in terms of the speeds of writing and accessing files. It depends on the situations of the markets, technology standards, user requirements, etc., but I think the most important factor is always budget.
NAND and DRAM can be employed to increase storage performance in various ways. Many of the latest Samsung SSD products offer, for example, features like RAPID Mode. Latest PC operating system software such as Windows 8.1 and OS X 10.9 Mavericks are able to utilize SSD technology in more creative ways though many of their innovative aspects were pioneered by third-party applications in the past.
RAID in both hardware and software have become first emerging, later popular, and redundant in more recent years. It was developed as a redundant technology to make better use of one of the slowest hardware components in PC and server. SSD in 2005 was not considered to provide faster sequential writing speed than striped SCSI HDD drives. By 2011 or so, even many of the cheapest SSD drives were reaching 200MB/s without need of being RAIDed. The norm in late 2013 is 550MB/s and I predict it will be between 1GB/s and 4GB/s in the next few years. Considering the rates of NAND evolution and commercialization into the form of SSD products in PC and server and other types devices, I judge RAID for most users has become redundant. There were many RAID users among the early adopters of Mtron and Samsung SLC NAND-based SSD devices. Capacity per unit tended to be 32GB and 64GB. 128GB was rare. That was when IOPS for SSD seemed to be the only benefit of adopting SSD (other than ergonomic and environmental considerations such as noise, energy consumption, weight, etc.) Most of them still use SSD as booting drive, but now as an independent volume.
If you want and need more raw performance, choose PCIe instead of SATA. If you want additional capacity for video files, add Thunderbolt or at least USB 3.0 external enclosure with a few 4TB or 6TB HDD drives inside. More RAM and more RAM for caching and RAM drive/disk are always good as long as the software is stable and reliable, but you have to pay double the amount of cash now then one year ago and it is only reasonable to expect at least some of the 20nm DDR 3 modules now being sold and not-yet-released 20nm and 14nm DDR 4 modules will cost far lower than ever.
SSHD is basically a combination of HDD + NAND + DRAM. Apple’s Fusion Drive is one such solution, but Apple moved to PCIe SSD this year though Fusion Drive was superior to other SSHD solutions. Seagate has, of course, different things to say: http://storageeffect.media.seagate.com/2012/10/storage-effect/apple-fusion-drive-or-seagate-sshd-is-there-a-difference/
My advice is don’t pay too much for a HDD (SSHD from my views is HDD, not SSD, a somewhat better cached HDD maybe, and there’s nothing such as a “hybrid”) and don’t pay too much for a SSD as it has already become ubiquitous and companies like Samsung have been very much committed to the technology having invested tens of billions in US dollars into the R&D and building manufacturing facillities so cost for superior specifications will continue to fall.