Processor speed or number of cores? -- which is more important in preventing system delays, etc.

Buying advice requested:

I want to get a MacBook Pro that will allow seamless multitasking that includes music software (Ableton Live, possibly Logic, plus auxilliary software such as plugins), together with:

➤ Office apps

➤ Browser (w- many windows/tabs open at one time)

➤ Windows via Parallels / VMWare

+ apps used within Parallels / VMWare

Can I get some advice as to which is more important in preventing system freeze-ups, slowdowns and delays:

• a quad-core processor (instead of a dual-core)

• a high GHz rating (instead of a lower one)

Also, a 5400rpm hard drive appears to be the only non-SSD option in a laptop. Is 5400rpm adequate to prevent the system problems mentioned above, particularly re: the music apps?

If not, what’s the best solution for that? Should I try to get drive replaced with an SSD drive? Or add an outboard SSD drive and use that as the main storage drive?

I'm aware that amount of RAM is also an important factor. I'm guessing 8GB is probably adequate: Is 16GB better, or overkill for the above usage?

Thanks.