I haven't figured how to quantify this, but after about a month my
impression is that for most sites, maxrequests=8 feels like a nice
improvement in browser responisiveness, relative to maxrequests=4.

However, for a few sites, the browser may 'choke' for several
seconds, as can be confirmed by watching the lxpanel cpu monitor.
I can't recall ever noticing this 'choking' effect at maxrequests=4.

My overall impression is that maxrequest=8 is (now) not the right number,
and intend to tweak it down some until the 'choking' isn't objectionable.