Performance increase with better mobo?

I have been looking around at hardware online for a while and I want to know something once and for all. Lets say I build a system for 3000$... how much faster will it perform Vs a 700 dollar computer? Is there a video somewhere of 2 DIFFERENT systems competing against each other in real time in actual everyday tasks? Reading benchmarks is fun but I never enderstand how this actually translates to real life... how many seconds are shaved off starting a game up when I buy a 180$ CPU vs one that cost 1500$?

Its things like this that make me wonder, if I make enough money in the near future should I spend the extra 1/2 thousand bucks on motherboards CPUs and water cooling to get only 4 more seconds of time out of a process?

Try Bit tech. They review some of the most recent motherboards in matters of HDD read/process speeds, overclockability, compatibility, features, etc.