This was my experience as well updating computers at a company I recently joined. Changing to an SSD had the most impact, although a lot of these machines already had 8GB of RAM. There are still a handful around that now have an SSD but still 4GB of RAM they came with; these are also better now, usable anyway.
My company did the same thing a while back. I remember two years ago having to get in the office at least 20 minutes before my z book laptop would fully boot.
They upgraded all the developer grade laptops with 32GB of RAM and SSD's. Still take a good 5-8 mins to boot, but compared to where they were? Light years better!
