Benefit of more ram with respect to processor speed?

[m6502]

RAM and processor speed accomplish different things. You need enough RAM to hold all your data in memory so it isn't swapping to disk. How much that should be depends on your applications, not what speed the processor is. Having too much RAM doesn't hurt, but it doesn't help either.
Disks are orders of magnitude slower than RAM, no disk can keep up with a processor, even the RAM can't do that in many cases. Good coding tries to keep data in local CPU registers to avoid the latency of accessing RAM, let alone a disk.

Intel's best P2 chipset (the 440GX) supported 2GB of memory, and some systems used glue logic to expand that limit further. ServerWorks chipsets on the P3 supported at least 4GB, some might have gone further, I'm not sure. It was possible to exceed 4GB in those days using PAE. But certainly nothing with that much RAM in the consumer sector though.
Some applications benefit from that much RAM - database servers for example. A more consumerish example would be raw uncompressed video capture. The most reliable, lossless raw video capture system I've had was an old P2 machine with plenty of RAM and monster I/O, most people probably wouldn't believe it unless they saw it in action.

But I agree that for most daily apps, you don't need a huge amount of RAM, and in my opinion it's the easiest thing in the world to upgrade later, at a cheaper price than what it costs today. One of the most important specs on any system, in my opinion, is the maximum RAM capacity (not how much is installed). This is one of the most under-reported specs and frequently the item that limits the machine's useful life. However, I don't think you have to worry about loading it up with RAM from day 1, it's easy to add it later - as long as it has room to expand. I guess many people won't know enough to realize *when* they need more RAM, though.

I wouldn't draw a relationship between CPU speed and optimal RAM size - the RAM you need depends on applications, that's all. The reason newer systems need more RAM is because they use larger/more bloated operating systems and software, not because the CPU is faster.