B757 FO EXCEEDED THE TURNING FIX LIMITS DURING A DEP SID DUE TO HIGHER SPD SHALLOW TURN MADE WHEN TURNING TO NEW HDG.

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I WAS RECEIVING OPERATIVE EXPERIENCE -- NEW ON B757/767. CAPT SUGGESTED USING LNAV FOR LOUPE 9 SID AND GO AHEAD AND CLEAN UP; BUT STAY AT CLEAN SPD FOR TURN. LNAV WAS ENGAGED AT APPROX 400 FT AGL; FLT DIRECTOR WAS FOLLOWED. AT 1.8 SJC DME; CAPT SUGGESTED HDG SELECT SINCE LNAV SEEMED TO BE INACCURATE. TURN TO 120 DEGS HDG WAS INITIATED AT 1.8 DME. DURING THE TURN; MAP DISPLAY SHOWED US WITHIN 4 NM OF SJC BUT RAW DATA ON VOR DME SHOWED 4.3 JUST PRIOR TO ROLLING OUT ON 120 DEG HDG. THERE SEEMED TO BE CONFLICTING DATA BTWN MAP AND VOR DME. IN THE FUTURE; I WILL NOT USE LNAV OR RELY ON IT TOO MUCH; BUT USE HDG SELECT AND GIVE MORE ATTN TO RAW DATA. ATC SAID NOTHING TO US ABOUT OUR POS AND I BELIEVE WE WERE IN THE LATERAL LIMITS OF THE SID (ACCORDING TO MAP DISPLAY). ALSO; CONTRIBUTING TO A WIDER TURN WAS THE SPD IN THE TURN WAS ABOUT 220-230 KTS. NEXT TIME; PERHAPS LEAVING FLAPS AT 1 DEG WOULD ALLOW A SLOWER SPD FOR A SMALLER TURN RADIUS. OR; PERHAPS A STEADY 30 DEG BANK TURN SHOULD BE ACCOMPLISHED IN THE TURN AND NOT USE AUTO BANK ANGLE FEATURE FOR FLT DIRECTORS WHICH CALLS FOR LESS THAN A 30 DEG BANK TURN.