No I never said that, your PSU will run the 280gtx fine. What I said is that you need to ensure that the rails are load balanced properly. In other words separate the various loads so that none of the rails gets overloaded.
I looked at the rail distribution more closely and the PCIe connectors are set up in such a way that there is really no balancing that can be done anyway, so no problem.
So although it won't balance automatically, there is no balancing needed or possible based on the rail distribution.
I won't get into the details, and further confuse the issue. If you want the details look at 4- Output Characteristics in the link above. I should have read it more closely earlier, and cleared it up at the time. My bad.