Extenders could be an issue, but they're wonderfully cheap and can even be used to spruce up the appearance a little bit.
I've got a 500d and had to get an extender in order to get the 8pin across the back from my Antec 650w PS, if I had left it it would have reached easily across the front...
I always like to have a bit of overage just so I'm not pushing the limit that things *could* hit. That said I OC the hell out of everything I put in my PC.
I'd be more concerned with the brand/build quality of a PSU than the watts, as a lot of the crappier ones can't sustain what they say anyway.