Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
I can't comment on the length of security lines at T4 at this particular instant in time. But is the lounge you're hoping to access at T4 pre- or post-security? And if it's post-security, are you sure that the TSA will let you pass, since you are not departing on a flight that leaves from T4?
In any event, if you immediately head over to T4 and are turned away, you should have no trouble getting back to T8 in time.