Good news for the SPC(P)s that are over 6 years (or in the Bravo Zone). You may now qualify for the same B Zone bonus as a SGT.

Retention Policy Message 06-04:
1. Effective immediately line 6B of MILPER Message 05-136 is changed to read: SOLDIERS IN THE GRADE OF E-4 or E-4(P) ARE AUTHORIZED TO REENLIST FOR THE ZONE B BONUS LISTED FOR SGT.

2. An update MILPER Message will be released soon reflecting this update. The RCP for E-4 non-promotable remians of 10 years and 29 days. The only nonpromotable E-4's eligible for the B zone SRB must meet the minimum reenlistment period and not exceed the RCP of 10 years and 29 days.

And here is the MILPER Message:
https://perscomnd04.army.mil/MILPERmsgs.nsf/All+Documents/05-312?OpenDocument