B737 CREW MISSED A DEPICTED TURN IN A SID.

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ACR ABC; LAX-EWR. WE DEPARTED LAX IN A B737-800 ACFT. IT WAS OUR FIRST FLT IN THIS PARTICULAR MODEL. VERY SOON AFTER TKOF; DEP CTL GAVE US 180 DEG TURN TO RETURN TO THE VOR; AS PER THE SID. USING THE SAME CRITERIA WE WOULD USE FOR OTHER B737'S; WE COMMENCED THE TURN. THE SID CALLED FOR XING THE VOR AT 10000 FT. IT BECAME OBVIOUS TO US THAT THE B737-800 MODEL DID NOT CLB AT THE SAME RATE AS THE SMALLER B737'S AND WE HAD TO WORK AT MAKING THE RESTR. DEP CTL ASKED US SEVERAL TIMES IF WE WOULD MAKE THE RESTR; AND WE TOLD THEM WE WERE TRYING. WE DID MAKE THE 10000 FT RESTR; BUT JUST BARELY. THE PROB AROSE WHEN I ASKED MY FO FOR LNAV. EITHER HE DID NOT SELECT IT PROPERLY OR DID NOT CHK TO SEE IF IT ACTIVATED. I FOLLOW STEERING COMMANDS ON MY FLT DIRECTOR; AND THAT LED US TO DEPART FROM THE SID. CTR GAVE US A TURN BACK ON COURSE; THERE WERE NO CONFLICTS WITH OTHER ACFT. WE APOLOGIZED TO CTR AND THEY INDICATED THERE WAS NO PROB. OUR WORKLOAD WAS SO INTENSE TRYING TO MAKE THEIR ALT RESTR; THAT I FAILED TO MONITOR MY FO ADEQUATELY. ALSO; THE FACT THAT WE HAD NOT FLOWN THIS MODEL B737 CONTRIBUTED TO OUR NOT BEING AWARE THAT THE CLB PERFORMANCE WAS NOT AS GOOD AS THE OTHER B737'S; AND DIVERTED OUR ATTN. DEP CTL WAS VERY PROFESSIONAL; BUT LIKE US; IF THEY HAD KNOWN THAT THE B737-800 COULD NOT PERFORM AS WELL AS THE LIGHTER B737'S; THEY PROBABLY WOULD HAVE GIVEN US A WIDER TURN AND MORE TIME TO MAKE THE RESTR; THUS MAKING OUR WORKLOAD EASIER. EVEN THOUGH THERE WAS NO PROB; I BELIEVE THAT A BETTER UNDERSTANDING OF THE PERFORMANCE OF A NEW ACFT RELATIVE TO AN OLDER MODEL; SHOULD BE BETTER UNDERSTOOD BY BOTH PLTS AND CTLRS. I APPRECIATE DEP CTL'S CONCERNS AND THE MANNER IN WHICH THEY HANDLED THE SIT.