The SSD will be the MAIN change in speed, not RAM. You will thank me after doing this and give your computer a few more years of usage.
The computer will work at speed of its slowest part - which in these days is Hard Drive with rotating/moving parts. Medium real (not advertised) access time for hard disks is 15 miliseconds, for SSD it is 0.1ms.
SSD can access files over 100x faster than HDD. You even don't know, but your system is working hard with many small files many times - add to it your activities, and bottlenecks are easy to arise.
I bought my first SSD when the performance was not that much better that HDD, and capacity/price ratio was sick. But later SSDs were cheaper, faster... Now I own 256GB SSD, but in terms of speed and smoothness of work I wouldn't like to see even 5TB HDD, thank you.
Now, changing from even "medium" SSD to medium "HDD" would be like selling Kemper and getting 5 PODs HD.