Nicolas, sweet and short!
danmcguire, your question was also curt and leaves room for interpretation.
First interpretation: When a user navigates the Moodle, will the (average) response time different (gets shorter) along RPi 4B 2G, 4G and 8G models?
This is what Nicolas answered. No, it won't. Because the RAM is not the bottleneck.
Second interpretation: If 10 users request a page from (click on) Moodle at the same millisecond, will their average response time different (gets shorter) along RPi 4B 2G, 4G and 8G? Same question for 20, 50, 100, ... users?
I haven't measured, but expect the response times to get shorter if these responses come from the (cabled) Ethernet LAN - assuming a quality router and network cabling, means an error-free 1 Gbit/s link to the router. I expect a less rosy picture if those devices are connected to the wi-fi of the access point of MoodleBox. Wi-fi is a shared medium with much more collisions than (cabled) Ethernet. And the experiment will stop any way when you pass 20 devices.