Can't believe people are still considering the ModXStream Pro 700W in 2013...
It is not a good 700W PSU, this is because it has a combined +12V rating of 552W and only 2 PCIe connectors. A good 650W+ PSU should have at least four. Which the TX650 doesn't have either.
So if you want to be able to upgrade to a multi-card config in the future then neither is a good choice. Also there are much better options available if you're sticking to a single card.
For a single card rig the Seasonic G-450 / G-550 is hard to beat for build quality and performance.
I would throw the be quiet Power Zone 650 / 750W in there as an option for multi card configs.
I'd even take the NZXT Hale90 650W over the Antec HCG-750M, as it has higher efficiency and much lower fan speed.