We don't have any official benchmarks to help you decide but I would recommend going with partial caching if you have areas which update dynamically. Partial caching is much much more flexible and reliable. I've used static caching on a couple sites and it is appropriate for a site thats designed in a specific way you can get a few quirks especially around pages with interactive elements, displaying comment counts etc.
As you said the static caching would get the best performance. Its only really limited to your servers ability so you can serve massive amounts of html without any issues.
I did a quick Partial Test vs raw SS vs static using apache bench over 1000 requests. (I'm not a benchmarking expert FYI)
For the sake of the test I did a checkout of branches/2.4. Installed on a new mysql DB. No extra modules. My environment is a 2.4ghz Macbook Pro, 3GB of RAM running Macports. PHP 5.3.2 and Apache/2.2.15.
I used ab -n 1000 http://localhost/silverstripe-core/2.4 for each test
2.4 default non partial cached over 1000 requests:
Requests per second: 710.87 [#/sec] (mean)
Time per request: 1.407 [ms] (mean)
2.4 default partial cached over 1000 requests
Requests per second: 797.28 [#/sec] (mean)
Time per request: 1.254 [ms] (mean)
2.4 default static cached over 1000 requests
Requests per second: 958.14 [#/sec] (mean)
Time per request: 1.044 [ms] (mean)
Hope that helps :D.