Installing Apache on another machine will increase latency (the request must go through another machine) and throughput (you also have more processor). Apache JServ Protocol (AJP) ( AJP on Wikipedia ) is useful to associate Apache with Tomcat and reduce the increased delay:
The AJP13 protocol is packet oriented. The binary format is supposedly chosen compared to more readable plain text for performance reasons. The web server communicates with the servlet container through TCP connections. To reduce the expensive socket creation process, the web server will try to maintain persistent TCP connections for the servlet container and reuse the connection for multiple request / response cycles.
(If you install them on the same computer ... to be honest, I never do this, but I would not think that there is a big difference in their SSL performance. In any case, if it is important, you should measure Do not miss the FAQ in Tomcat Wiki .