You'll be able to fit a Noctua NH-D14, which is the probably the best air cooler you can get right now. You'll lower temps a bit, whch may in turn lower noise but noise itself is due to the fans. Now if temps are lower the fans should throttle back for less noise, but ultimately if you have quiet fans it won't change much in terms of noise. You'll see maybe another 3-5°C difference, whether that's worth an $80 purchase is up to you. You can probably squeeze another few more degrees if you go to a H100/H100i, but you still have to purchase quiet fans.
You want performance and quietness? Go with custom water cooling.
EDIT: I noticed you said you were on stock voltage. Why are you worrying about heat if you're not upping the vcore? You might be able to eek a bit more performance at stock with cooler temps but bumping up the voltage will give you a lot more result (and heat).
San Francisco: Gigabyte GA-Z77X-D3H | Intel i5-3570k @ 4.5ghz | 16 GB DDR3 @ 1866 | Gigabyte WF3 7950 @ 1125/1500
Honolulu: Gigabyte MA790X-UD4P | AMD Phenom II X4 955 @ 3.8ghz | 8GB DDR2 800 | Sapphire HD4890
London: ASRock 4CoreDual-VSTA | Intel Dual Core E7400 @ 3.1ghz | 2GB DDR2 667 | ATi X850 XT @ 540/590
Last edited by Eureka; 11-13-2012 at 10:54 AM.