Which processor is "better" kind of depends upon what you expect from your laptop. There is a web site you can use to review and compare the features & specs of these two processors side-by-side. Please see the features comparison at the following link: http://ark.intel.com/Compare.aspx?ids=40480,43122 http://ark.intel.com/Compare.aspx?ids=40480,43122.
In general, here are some ways you might differentiate the two processors you are trying to compare.
While both of these processors you are asking about are quad core processors, the Intel Core i7-720QM processor features hyperthreading (4 cores, 8 threads) while the Intel® Core™2 Quad Processor Q9000 does not feature hyperthreading (4 cores, 4 thread).
The Q9000 is a 2GHz CPU (max frequency), whereas the 720QM is a 1.6GHz CPU that features Intel turbo boost technology and can run at up to 2.8GHz (max turbo frequency).
These two processors are not socket compatible (not interchangeable). The http://download.intel.com/design/processor/datashts/320390.pdf Intel® Core™2 Quad Mobile Processor (9000) supports the Mobile Intel® 4 Series Express Chipset Family. The next generation http://download.intel.com/design/processor/datashts/320765.pdf Intel® Core™ i7 Mobile Processor (i7-720QM) supports the newer Intel® 5 Series Chipset.
Both of these processors are intended for systems with discrete graphics, they each feature 6MB Cache, and each has a max TDP of 45W.
Processor NumberQ9000i7-720QM# of Cores44# of Threads48Clock Speed2 GHz1.6 GHzMax Turbo Frequencyn/a2.8 GHzCache6 MB L2 Cache6 MB Intel® Smart CacheSockets SupportedPGA478PGA988
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If you have teh choice and the price difference isn't that much i would for teh i7-729QM, newer technology, more threads and with turbo boost higher clock speed when needed, probably better power management too.
don't worry about teh overclocking as you don't really do that on a laptop anywyas, normally they won't have teh cooling for it.