PSU upgrade question.

[Googolplex]

The CPU should have the same power consumption as your old one. A CPU will use something between 75 and 100W at 100% load. 450W is enough for the complete system!

And I doubt that the Athlon X4 will be much faster. Of course it's only faster when an application can handle all 4 cores! But only some modern games are using multiple tasks. Your current CPU should be fast enough for 720p video rendering.

When you want to convert movies etc. I recommend to upgrade to an Intel Core i5-4570. It's a lot faster.