How much does i5 1.7gz and i3 2.0 gz differ in speed and which is preferable if i5 have 8gb ram and i3 4gb

[Gr8_ari]

Notebook
How does the clock speed matter
And
How much ram maters

 

[rgd1101]

what is the exact model? there a 6 different generation and hundreds of different model of i5/i3.