The old G5 was a rock solid mouse, even though it's too heavy to my liking without any weight(using razor diamondback currently, my copperhead crapped out last night, button 2 failed). Also the wheel button was a joke. You have to really be careful to press it without moving the wheel up or down. For this reason alone I would suggest to get the newer version.
From the sound of the review, it seems that they fixed the wheel button problem. But it seems like the weight stayed, cuz they looked exactly the same.