Overhead of using SSL?

jedinite writes "I'm currently heavily involved in a project to develop a specialized online community. We've hit a serious debate among the team regarding whether or not we implement the site using SSL.

Basically, there are two schools of thought here: My side, that privacy and security are the most important, and we're willing to take the performance hit, and the Other side: that the use of SSL will "devastate web server performance" - that the trade off of security for speed is necessary. My question to the assembled masses: What are the potential upsides and downsides of using SSL on a (relatively) high-traffic site? Anyone have any better metrics on the real difference between unencrypted and SSL traffic? Can anyone here help me convince my team that we need to use SSL -- or convince me that we don't?

More info on our situation, if it helps:

We're running a four-way Sun E450 with 2gig of RAM. Big, big box.

We're running Stronghold/2.1.1 Apache/1.2.4 mod_perl/1.11

We're anticipating approximately 50k-60k "hits" and about 5k-6k page views on the community daily.

The box handles about 3 times that traffic total (other sites on same box). "

Another "solution," other than the all or nothing approach, would be to use a "shopping-cart" type setup. You know, the bulk of the site is non-SSL and the switch to SSL is only when there are items to be protected. Other suggestions and comments?