I have an AMD Phenom II P960 quad core with 5400 rpm HD and 4GB ram. I do mostly web based stuff with several things going on at once. Will switching to I5 dual 2450M processor with 6GB ram be faster?
There really is no AMD CPU right now that is as fast as or faster then the Intel I Core processors right now.
But a quad phenom II will be faster than a dual i5 in many situations. Multitasking suits a quad, but with web browsing you won't notice the difference.
For general use, the most important speed factor is the storage because this affects boot and application launch times. An SSD upgrade would have a transformative impact on your computer but it's an expensive upgrade.
Since these are notebook procs, I imagine you're talking about buying a new laptop or not.
I'd go with not. You can almost assuredly switch out the existing HDD for an SSD for far cheaper than a whole new unit. That said, you have to question performance vs. capacity vs. price (SSDs are usually much smaller than HDDs capacity wise).