I've never seen 2 seconds be a problem on localhost. That's the reason it's configurable in the first place. If it takes 5 seconds to get a response on localhost I'm not sure what would cause that. Is your server overloaded or something? Are you using windows client with full IIS and the 10 concurrent connection limit? Why not make it 7 or 8? 

I think our default shouldn't be too long (5 seconds may be fine but it was chosen randomly by you based on your experiments on a single machine in a single environment. That's why I'm skeptical.