The stealth (?) Cooler is not very large. You can undervolt to 1.15v, it barely goes above 40 on my aftermarket cooler. I tried to improve my boosting - nothing to write home about. I has getting 80ish during prime95 in an antec p180 at 1.25v with the stock cooler; no info undervolted.
I only managed 1741 fclk/mclk on mine and it won't do 4.2ghz on 1.4v. I think they binned these properly! Pretty good value for £85 though.