If you haven't had any problems with heat-related crashing, you are probably fine, since you don't plan on O/C'ng anything.
On another note, that 450w Antec PSU, does it come with the Sonata case? If it does you're pushing the upper limits of the PSU with that beefy system. Those Antec PSU's were nice a couple years ago when the systems weren't dual-core, but most dual-core systems SHOULD be powered with at least 500 true watts, IMHO. It would still work, but it will burn out faster than a PSU with more headroom, and that can get expensive.
You should be just fine. I doubt that system will draw more than 350 watts under full load so your PSU is more than enough. With out overclocking the stock cooler will be sufficent but you may want to replace it with a quieter one.