Question with a new rig

I want to update my old 4 year rig...it has:

Phenom II X3 720 BE @ 3.0Gzh.
Asus M5A97 970 Chipset
Sapphire HD 5750 Vapor X
4Gb DDR3 1333 + 2gb DDR3 1333 Kingston Hyper X
500Gb Wester Digital Caviar Black Sata III + 1Tb Samsung Sata II
Cooler Master TX3
NZXT Lexa S
Pixxo Jaguar 600Watts (its like an Cooler Master XPP "600 watts" but max 430 watts) it plays nice tough.

I wanted like many to update to AMD FX since i have used Atlhon XP, Athlon 64 3200+, 5200+ but since i have waited a long time and updating to FX would be 0-10% better i want to change to intel....i have at least 600 bucks and i have this config in mind:

Core i 5 2310 (a little cheap in here as good as the 2500k but without overclocking capacity)
gigabyte p67 board (i dont remember the model but is mATX...a little sad having now an 970 chipset)
HD7870 (i will buy this later since now im playing at 1366x768 and almost everthing i play runs at max)
i will add a SSD later this year since their are extremely expensive in mexico
Ram reamains the same, as HDD Case and for a little while the psu.

My questions are:

The Core i5 2310 cost me about 180 dollars but the 2320 is 20 bucks more expensive and the 2500k is 270$ but i can buy it since the mobo cost about 100 bucks.

How many performance improvement will i have over the 2310?

What is better the 2310 or 2320?

is true that the P67-z68 is more for K proccesors and i should buy an H61-H67 motherboard for the non K proccesors?

Would be better to wait for Ivy Bridge?