The HDD is the biggest bottleneck to most systems. Sounds like you would see little difference in increasing cpu speed/cores based on what you are doing.
The SSD will make a big difference in loading your OS (cut down boot time) and improved load times for programs. It will NOT speed up in-program performance (ie improve fps in games). It wil NOT speedup downloads and brossing the web.
That Said, I love my SSDs have them in two desktops and twolaptops.