CEOs are more like high ranking general officers, not O-6 level (Navy Captain, Army/Air force full bird colonel)
O-5 (Lt Col, Navy Commander) would be VP / GM level stuff, GS-13 through GS-14 in the federal government
O-6 equivalent in the civilian world equates to a GS-15 in the federal government, and a senior VP in the corporate world
O-7 (brigadier general) would be an EVP level position, C-level large org
O-8 (general) would be CEO