An SSD upgrade is still the single best thing you can do for your PC
I can't tell give you exact numbers because I don't know either your computer or what SSD you'll buy. But I can tell you this: The hard drive, with its mechanical moving parts, is almost certainly the biggest bottleneck in your PC. (If it isn't, you've got something seriously wrong--probably in the software.) Replace that hard drive with an SSD, and the bottleneck disappears.
[Have a tech question Ask PCWorld Contributing Editor Lincoln Spector. Send your query to firstname.lastname@example.org.]
Back in 2013, PCWorld Labs ran three computers through our WorldBench tests, then replaced the hard drives with SSDs, and ran the tests again. The results were astounding. A Toshiba Satellite P75-A7200 increased its WorldBench score from 279 to 435 (a higher number means a faster PC). A Maingear tower PC doubled its score from 162 to 325.
But those are just numbers. Let me tell about my own experience.
When my laptop had a hard drive, I would come into my home office every morning, power it up and do 40 shoulder rolls to limber up. Just as I was finishing, Windows would ask me for my password. I entered it, then left the office to do some household chores. When I returned, my computer was ready to use.
I replaced the hard drive with an SSD in the spring of 2014. Now I power up the computer and start my shoulder rolls. At about roll 17, Windows asks me for my password. By the time I finish the rolls, it's just a matter of seconds before my computer is ready to use. (I now do my chores before I step into the office.)
And that's just the boot process. When I had the hard drive, I would load Photoshop Elements before I needed it, because I didn't want to wait for it to load. I've since lost that habit, as it now loads in seconds.
Of all the performance-boosting upgrades you could do for your PC, an SSD offers the biggest impact. But before you make the transition, you may want to read up on gaining speed without losing capacity, and--if you do have to lose capacity--on making the transition to a smaller drive.