How will a VP450P respond to a stock i5 with a 650 ti boost, and how will it hold up with slight GPU overclocking in the future?
A good supply over 400W is enough for your system.
The Antec VP450 is actually very good for the price, but not as efficient as better supplies.http://www.hardwaresecrets.com/article/Antec-VP450-Power-Supply-Review/1487/11
If the VP450 is the most you can afford, it is a good choice.
If you can afford spending a little more, look at the Seasonic S12II 430.