I just checked and I have the same setting on Silver... Here is what I found about the limit on the cPanel site. Setting the right limits for shared hosting
Stan you must have a very active site
ENTRY PROCESSES (Concurrent Connections) Limits the number of concurrent connections and cron jobs that an account can have at any one time.
Each time someone connects to Apache, a connection is used up. There are a limited number of slots in Apache web server for these connections (specified by MaxClients). It is set to 150 by default but often increased to 1000 or more on shared hosting servers. While connections are quickly served for static pages, dynamic pages take their time.
CPU throttling can cause such pages to take even longer to serve, tying up even more slots. Once all slots are used up, apache will not serve any new requests until existing requests are processed, bringing the whole server down. To prevent this issue we added another parameter that limits the number of concurrent connections a site can have. The default is 20. If a site has more than 20 concurrent connections to dynamic pages any further request will receive a 508 error (resource limit reached.)
It is important to note that concurrent connections are not the same as concurrent users. The majority of applications such as blogs, forums, etc., consider a user to be someone who visited a page within past 15-30 minutes. So, 300 concurrent users on the forum might mean only 5-6 concurrent Apache connections.