Desktop

As ASUS has quite a few in the P8Z77 lineup. Not sure which is the exact one you have but the M Pro which I'm assuming is what you have supports the following CPU's

Intel® Socket 1155 for 3rd/2nd Generation Core™ i7/Core™ i5/Core™ i3/Pentium®/Celeron® Processors
Supports Intel® 22 nm CPU
Supports Intel® 32 nm CPU
Supports Intel® Turbo Boost Technology 2.0
* The Intel® Turbo Boost Technology 2.0 support depends on the CPU types.

The increased speed of the Suggested CPU will see a performance increase but that depends any many other things like the Amount of RAM used the type of OS in use and so on.

Basically any 32 Bit OS can not address more than somewhere around 3.25 GIG of RAM depending on the Chipset involved some chipsets support larger RAM Loads but regardless if it's a 32 Bit OS it's not going to see any more than 4 GIg and even then may not produce the best speeds possible.

Then depending on the RAM Configeration performance can vary. The above M'Board has Dual Chanel RAM so 2 Matched X 4 GIG Modules will perform faster than 1 x 8 Gig Module or some other uneven configeration. You need to install any RAM in Matched Pairs and then in the correct Sockets for best performance you can not just dump the RAM into whatever socket you think is empty and expect the best performance.

On the Plus side the RAM Sockets are colour coded and the Destruction Manual fairly detailed on this issue and is easy to setup so if you have the M'Board properly setup and a Suitable OS then moving to a faster CPU will make a difference but how much I'm unable to say.

I would suggest you a MSI Z170A KRAIT Gaming for that 6700k but as for right now i would wait a little longer so that 7700k motherboards spread a little across the market and that is how you'll get the latest and fastest technology.