Is a CPU upgrade from an Intel i3-370M to an i7-640M worth it?

[rasburicase]

I own a 10 years old HP dv6-3114sl laptop, recently upgraded to an SSD and previously also to the maximum amount of RAM supported, that is 8GB. I can say that everyday use is enjoyable, expecially I note differences opening the browser and while surfing.

When in the past I disassembled my laptop to fix the cause of an overheating and consequential fan noise, I discovered that my CPU is easily changeable. I have an Intel i3-370M with an integrated Intel GPU. I thought to squeeze out the power to the maximum from this old, but still working perfectly laptop, with a small cost before passing to a brand new one.

So I searched my Intel i3-370M on cpu-upgrade.com and then the list of compatible processors. I found that the CPU with identical charachteristics is the Intel i7-640M. They have the same microarchitecture (Westmere), same socket (G1), same number of cores (2), same number of threads (4), same stepping (K0) and same TDP (35W). Above all I can find it on the net at a reasonable price of 40 USD (shipping included).

So at the end... what's the problem with it?
I read the maintenance and service guide of my laptop series and I didn't find the i7-640M listed under the processor chapter. I've seen listed instead other kinds of i7 such as: i7-720QM, i7-740QM, i7-820QM and i7-840QM. But these are quad core CPU, have another microarchitecture (Nehalem), a greater TDP (45W) and haven't the integrated Intel GPU. I don't realize why they're supported and why the Intel i7-640M (that seems too similar to the i3-370M!!) is not.

The last consideration: I found out also an extreme i7-940XM CPU of the same Nehalem family, with the same carachteristics of those previously listed but with a much greater TDP (55W). Obviousely it's not listed in the maintenance and service guide.

After all, which is the best choice I could make? First of all, is a CPU upgrade worth it? Then, which CPU would be better to buy: i7-940XM, i7-840QM or an i7-640M?

Thank you all.

[Repairatrooper]

If you look at the guide, there are many different main boards used in this series with different features such as discrete graphics instead of integrated graphics. Chances are the board shipped with your product will require a processor that supports integrated GPU. If the processor you want to use is not listed and you can find no documentation of anyone installing this cpu and having it work then you will be the guinea pig for everyone else. If you are comfortable risking the $40.00 you might want to try.

[rasburicase]

My motherboard came also with an ATI Radeon GPU, so I guess it can support also i7-840QM that hasn't got an integrated GPU, but in this case I think I should change also the heatsink/fan system to sustain a 45W processor.

Many elements are in favour of the Intel i7-640M.