I would go for the antec earthwatts 650 watt for around $75 to be safe. Modular is nice, but not necessary. More juice is better, and those modular cables may have trouble reaching any bottom mounted power supply which is common on newer cases.
Keep in mind that the Earthwatts do not come with a power cord and Antec cases do not come with a system (case) speaker. And if you want to do a neat job of cable management and run the power cables behind the motherboard tray, the PCI power cable probable will not reach without using an extension cable.
The Antec 300 has a special compartment for cable management so if you you get a non modular PSU like me you can out extra cables in it. Also the PCI-E cables from my XFX PSU go through the cable compartment therefore they should really be long enough to go under the mobo. You would just have to check the difference in length of the cables of my PSU and the one you will buy.