All of this is good, but there is one question I don't see addressed. you had referenced that actual application resides elsewhere on your network. Have you tried putting that specific host in a dedicated broadcast/collision domain? Is it on the same segment with the other clients?
Not only do you have to be concered with the actual link usage by the requests coming through the router, but what about the basic physical problems like collision domains?
If the clients are using the router at 30-40%, no worries on the router side, ISPs have confirmed that 512/512 adn 25 users is OK. Personally I have to integrate a nationwide network and we have hundreds of Citrix servers. None of which have given me the same problem. A lot of that is due to the fact these servers are used implicitly for the applications that reside on them, or a reachback shortcut to the network share that hosts them. Again, this design supports server farms and dedicated bandwidth to the actual server that hosts the application.
What about media contention?
Bottom line in case I confused anyone,
CSMA/CD. You may not be overworking the router, but depending on your LAN structure inside, the application server may be dependant on Media Contention with regular user host workstations. If these people are checking mail at automatic regular intervals or accessing network shares, this will degrade your throughput extensively as the server must SHARE the bandwidth of the local subnet. Just because the router doesn't support 100 MB on the interfaces, doesn't mean that internally you cannot run 100MB from the server to the switch. Dedicating this segment will give the server full access to it's media. Let's the router worry about handling the amount of return traffic from the server.
Good Luck.
