No one is going to argue that his power supply is great. But he's on a budget and wants to know if it'll run with a gtx460. My advice is that it will. Yours is that it may be unstable above 300w and that it's inefficient. Interesting? Yes. Critical to whether this guy on a budget can try running a gtx460 in his system? No. If he wants to overclock then yes, he should get a better psu. And I don't recommend the 1GB gtx460 for him because it uses 20 extra watts and the extra cost will not bring him any performance benefits.
No one is pointing out his power supply is bad. The StealthXStream, while not excellent, is good and much better than the Cooler Master.
He also made no mention of what his budget is and all that it entails. Hence why I offered my opinion of the situation. It's more than just "interesting", so please don't downplay the significance.
What's ridiculous is that some people here were recommending he get the GTX 460 AND overclock on that power supply. That is just not safe; not safe at all. So if you don't think my advice was critical in this regard, then you need to re-examine yourself and stop being controversial. He would be putting his entire system at risk doing what most people here advised him to do.
The significance of a higher efficient power supply is that it is quite possible it will pay for itself, or greatly reduce its cost of operation, over its lifetime. And he does live outside the US, so there is a good possibility he's paying a lot on the electric bill. Which means an efficient PSU will be of even greater cost benefit, as well as adding safety for his components.
I'm not really concerned about what video card he can get. I think it's wiser to invest in a better power supply. But if he can have his cake and eat it too, then that is obviously the best route. In fact since he wants some longevity out of his system, spending more is the only way to do this. And I think it would be better to get the power supply now, and then get a video card whenever. And you will say differently. There is nothing more to this than that.