should i buy the GTX 1070 if i have the i5 2310?

Well its a good GPU even if the processor is crap, You can have it on the system but it might not be used to its fullest, but you can easily put the card in a new system if you end up upgrading the processor / motherboard

Core I5 2310

Haha, Intel hasn't really come that far with their CPU's. Overall the i5-2310 isn't that much slower when compared to the newer Core i5-6600. Clock speeds being equal, the IPC increase between the 2000 series and 6000 series is around 15% to 20%.

Sadly, the 2310 is locked to 3.2ghz in Turbo mode. If you had the 2500k, a simple overclock would erase the gap.

I wouldn't say i5 2310 is weak CPU, but I guess it will also depend on games you are trying to play

Newer CPU intensive games like RTS or simulators may be bottle-necked by it

But most of graphics intensive games should be fine, like Rise of The Tomb Raider, Far Cry

I have 2500K, running at stock clock of 3.3 GHz, and I don't see it bottlenecking my GTX 970

If the GPU ends up waiting on the CPU a lot then you just upgrade the CPU later.

My last GPU upgraded ended up with the GPU only being used about 10% in most games until I upgraded my CPU to an i5, now my GPU is maxed out in most games and needs upgraded again.

why are all the answers so short these days?