I have a Pi3b in a 3D printer, and compiling the software, but also simply apt upgrade feels like it takes forever. Most day to day operations work just fine though.

At work we have a display with a Pi3 (not B) connected, just showing websites in rotation. Websites even with a simple animation are laggy, startup takes a few minutes.

Both of these usecases don't need more than 1 GB of ram, but I want to speed of a 4 or 5.

Usually it's just "same thing but faster". CPU is 2-3x faster, and even boot speed is faster, so it can be handy to not have to wait so long to run updates, compile something, reboot, etc.