Processor Speed vs # Cores

[idata]

I've been looking around at laptos pnile and have a few general questions about processors.

While the Intel Core i7 processors claim to be the fastest mobile processors, I've been noticing that they often have lower GHz than other processors, even other i7 processors that have fewer cores. For example, I was viewing a comparison between two laptops with the following processors:

Intel® Core™ i7-640M Processor (2.80 GHz, 4 MB L3 Cache)

Intel® Core™ i7-740QM Processor (1.73 GHz, 6 MB L3 Cache)

The second processor is a quad-core because of the QM, right? Yet it only has a frequency of 1.73 GHz, while the duo-core has a higher frequency of 2.80 GHz. The second does have more L3 cache though. Which of these is the better processor?

I saw this laptop as a possibility for myself: http://www.staples.com/HP-Pavilion-dv7-4190us-17.3-Laptop/product_904966 http://www.staples.com/HP-Pavilion-dv7-4190us-17.3-Laptop/product_904966

While the storage space is more than I need, everything else seemed to make it a high-end and efficient laptop. It has a Intel® Core™ i7-720QM Processor, which I found has 6 MB Cache. This processor has a pretty low GHz level also, though. How does memory affect the performance? It has 6GB of installed memory, which I think is pretty good.

I'm looking to buy a new laptop because of serious performance issues with my current one, which is about 5 years old with an Intel Pentium Dual-Core inside. It was a low-end laptop from the start, and the operating system is only registering about 433.2 MB of memory. I want to make sure that I will definitely see an improvement in performance and speed with the new laptop I choose. Any guidance would be appreciated. Thanks!