There might be a ROM in this forum that enables overclock. Otherwise, you will have to visit XDA http://forum.androidcentral.com/htc-hero-roms-hacks/9867-all-sprint-cdma-hero-roms.html and download a ROM with overclock built into it, or flash the update.zip to enable it. In short, yes it will make the Hero faster. It's been achieved with an updated kernal (.29) that was ported from the Eris and made to fit our Heroc.
Yes Beezy420 made both koolaid and honeybun ROMs where you can flash an update that allows for overclocking. in the thread for overclocking 2.1 there are instructions on how to. any questions please ask there.
Having been on that linked kernal for awhile, I would actually suggest against it. It created problems with the dialer (answering calls, and sometimes even hanging up), and closing wifi tether.
as that has given me overclock and kept stability all around.
Note, having tried many different roms (here, and on XDA), I have found the most stable rom (overclocked or not) to be honeybun. It's extremely close to stock, extremely stable, and I no longer have the frustrations of "why is it doing that???". And I am overclocking it. I really need to remember to donate to beezy for an incredible job.