Just curious, but I recently bought a new cpu with 8GB.
Before I installed the additional memory I had purchased, I rendered out a previous project in AE that took 13 mins. After installing 32GB of RAM, I rendered out the same project and it only saved me a whopping 3 minutes in difference.
What would I need to see a major difference? Like half the time?
I currently have a 27" iMac, 3.5 GHz intel Core i7 processor along with a NVIDIA GeForce GTX 780M 4GB graphics card. A 3TB Fusion hard drive as well. Oh....I'm using Creative Cloud.
Same as all the other performance-related threads: More memory doesn't make a difference if no effects are used that can benefit from it or plus all the other things like specific CoDecs or temporal effects forcing AE into single-threadedness and all that. Do a search.
Impossible to say or predict without knowing every detail of your Composition, your source footage, your Render Settings, Your output module, and without running tests on various memory configurations. If you have not changed anything I think that the about 25% reduction in render time would be about right. A HD frame is only so big. You can easily have more memory than rendering a frame can use.