Here's roughly the jist of it:
Corsair K70 - This is the keyboard best loved by many people. It has a much wider choice in colours, switch types and LED colouring. Pretty much every keyboard in the Corsair mechanical line features the same heavy aluminium design, both the K70 & K95 are no exceptions.
Corsair K95 - This is basically a K70 with an extended bit on the left side for Macro's. You'll have to decide if it's worth the extra desk space. Macro's allow you to program them to do an action when you hit it. This is why it's marketed as an MMO/RPG keyboard, because you can use them in the crucial moments to switch weapon or something.
It's basically a K70 with that extension. There are two important differences though -
1. Only white LED lighting (There is an RGB version coming very soon, but it's likely to be expensive).
2. Only Cherry MX Red key switches. I really like my K65, but I do so wish I spent a bit more and went for a tactile key switch. The red is linear (Supposedly better for gaming).
Other than that, aside from price, they're all but identical. If I was making the same choice my brain would be telling me to get the K70, but my ego would be saying "Yooo, dat K95 will look l33t on ur desk brah". Due to its larger-than-most design.
Word of note btw, there are multiple stories of the LEDs on both versions failing, supposedly put down to static, due to the all-metal frame. This is going to be adressed in the RGB line coming out soon due to the way they're placing the LEDs inside the key switch itself rather than right next to it. Like I said though, they're not out yet - and they're likely to be expensive.