Difference between r egular 2.5 and 3.5" hdd

Hey. i wonder. lets say could choose from these two:

WD Mobile Black 500GB 2.5" with 7200rpm 16mb chace sata 3 6gb/s

and

Seagate Barracuda® 500GB 3.5" 7200rpm 16mb chace sata 3 6gb/s

Thinking about that i am going to buy a Corair air 540 this is a huge thing,

i am going to use an ssd for OS and Some games and programs

If there is a huge performance differance between regular 2.5" and 3.5" then what?

Thanks