"I would like to know if hard drive access speed is a bottleneck to my system currently."
Of course! There are two aspects to a disk storage system:
- Bus speed
- Storage medium speed
On ANY given bus, e.g., SATA, SATA2, SATA3, a mechanical HDD will be an order of magnitude slower than an SSD for a given link speed. The secret is to always use an SSD that features at minimum the same link speed as the disk controller. It can be of benefit, however, to use an SSD (or HDD if you're financially challenged) that features a faster link speed than its host.
For example, I'm using a Crucial M500 960 GB SSD in my MacBook4,1. The SSD is a SATA 3, 6 Gb/s drive, whereas the MacBook has a SATA 1.5 Gb/sec controller. The drive performance is marginally (!) better due to its higher internal processing speeds than would be a 1.5 Gb/sec SATA SSD on the same system.
Mechanical hard disks are painfully slow compared to their SSD counterparts. In ANY computer system, the HDD and its attendant controller will be the biggest bottleneck. As such, to ensure best performance, you should use the fastest storage medium possible.