Ok, I've taken apart my case to check this myself. I have both 4 pins connected and they're in the same bundle of cables. More so, they actually turn into a single 4 pin later. However, you have to connect both 4 pin connectors as each supplies half of the 6pin connecting to the GPU.
Why it's a 6pin into 2x4pin? I'm not too good in this but I think it's better to use 2x3 out of 2x4 cables instead of somehow changing 4 cables into 6? Remember that with a 6pin to 1x4pin you'd be missing 2 cables ( or whatever's the name for this ).
Btw. I'm running OCZ StealthXStream 500W, too. It's working fine with a 4870 that, according to reviews, is one of the more power hungry versions. There's also an overclocked and unlocked Phenom II x3 720BE and 4GB of oc'ed DDR3. From what I know, this particular processor of mine is also rather needy in terms of power.
