Looks to me like that's the only difference. The 3973 is a stock-clocked card, and the 3975 is an SSC model, with 140MHz faster clock speed. 

The 3975 ssc will probably OC better because of the 6 and 8 pin power connectors. I've got 3 of the ssc and think they're value is worth the extra $30

According to the specs and pics they both have 6/8 pin connectors, dual bios and optimized power target. It looks to me that the only differences are the ones I mentioned. I just wanted to make sure with you guys. I think that the 04G-P4-3973-KR can be overclocked to get the same performance of the 04G-P4-3975-KR. I'll pick the 04G-P4-3973-KR to save some money. Thanks guys!

BigLouis1971
Watching at the specs alone the difference I see is the core/boost clock and the texture fill rate. Is there any other difference that can't be seen by watching at the specs like a custom PCB or PCB layout? I'm about to get either of those cards and there's a price difference of about $30 after rebate and if there's not a big difference beside the ones mentioned, I'll pick the cheaper one. Thanks in advance!

Generally, custom pcb doesn't change anything unless doing low temperature overclocking. They may occasionally overclock better on air or water, but it doesn't change all that much, especially with the current generation of GPU's.

With the factory over clocked cards, like the regular model, SC and SSC, you will see differences in games, as they will have use of the higher stock clocks. If you are just at the desktop, or watching videos online, nothing will change.

The 8 pin will possibly allow for more overclocking and a more stable stock card, but that isn't a guarantee either.. It is all up to the Silicon lottery in the end. :-) I would say go for the higher clocked card, just because it is only $30 and not all that bad of a difference.