Intel Pentium D 830(3.0GHz Dual Core) bottlenecking

Forgot to mention he's upgrading his ram to two 2gb slots of DDR2 ram (total of 4 gb), and his motherboard does support pci-express. The only thing giving me any hesitation telling him to order the card is his cpu as I don't want him to order it, be unhappy and have to upgrade his cpu as well.

He needs a full system rebuild. Anything before Core 2 or Phenom II is not worth spending more cash on. It simply isn't worth it.

I had a feeling as such but he doesn't really want to listen. As long as he can run it pretty comfortably (on medium) he'll be happy. He was pretty hesitant to spend more than 50-60 bucks on a new GPU before I told him it's a necessity. He's not really looking for future upgradability, just that right now he'll be able to play Diablo 3 without giant headaches.

Do you think that this card will see severe bottlenecking with this processor? I know it's old, and I heard somewhere (can't remember) that it's not actually a true dual-core processor so that's why i'm asking.

Of course it's a dual core processor but unlike modern dual cores it has two dies instead of one. I say get the 6670. Who cares if there is a slight bottleneck it will improve game performance and that's all he wants.

I would say that the Pentium D @ 3.0GHz will have an equivalent performance as a Core 2 Duo CPU @ 2.4GHz or 2.5GHz. Not blazing fast by today's standards, but good enough not to bottleneck a Radeon HD 6670 (or at least not by much).

The greater concern is that your friend has a motherboard with a PCI-e 1.0/1.1 slot. All Radeon HD 5xxx and 6xxx series graphic cards are PCI-e 2.1. There have been a few incidents where a PCI-e 2.1 card will not work in a PCI-e 1.0/1.1 slot. The chances of your friend's mobo does not support a PCI-e 2.1 card is low, but the possibility is still there.

Basically the only way to find out is to try it. Unless you know someone with the exact same mobo and attempted to install a PCI-e 2.1 card.