ok that answer al my questions, thanks. So you would go for the 4x 270s or 2x 280xs? Brand=MSI?
Please translate this for noob minners like myself: I got the gigabyte 270s as they have 2 6 pins which allow for HUGE OCs (all the sliders to the end of after burner and further after unlocking OC limit)
Oh sure, the 2 6 pins allow for more power to flow to a card so the card can access more power when it needs to (which it does when you OC it) and with 1 6 pin the card might be unstable as it doesn't have enough power going to it but the gigabyte does as it has 75W more power to hand as it requires.
Yes, I would go for MSI on the 280X as it is cheapest and gets 650K/hash with a mild OC and I=18 (don't know about other makes for 280X but gigabyte, MSI and sapphire toxic is recommended for the 280X)
For 270s again I only have experience with gigabyte, but I have heard that gig cards get good OCs (which they do) and I think they are the only 270s with 2 6 pins and the only one which can get to 450K/hash without breaking a sweat (Again not 100% sure if others can or not) but that is IMHO.
Gigabyte=270 (NON X)
MSI/TOXIC/GIG=280X
Risers are what you put in the 1X and 16X to extend them off of the motherboard which allows for the air to flow better so they won't be touching (look on ebay for PCI powered risers) also they have to be powered if you don't have a mobo for mining (I.E BTC pro gigabyte)
The gig 270x require more PSUs as they have 2 6pins (if you just want 3 or 4 one PSU would do (1250W+) but I went for 2 X 750W EVGA supanova as that worked out cheaper than buying one big one, but they can only support 3 cards on each (even if they have more power they can ouput) as they are limited by the PCI outputs from them
Any more help just ask.