B767 FLC MADE A MISSED APCH DUE TO BEING UNABLE TO MAINTAIN SPD AND GS DSCNT PROFILE DURING AN ILS APCH AT DEN.

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ON APCH INTO DEN; THERE WERE RPTS OF VIRGA AND LLWS. MANY SCATTERED RAIN SHOWERS ON THE RADAR. DEN WAS CHANGING RWYS FREQUENTLY AS THE WIND SHIFTED. WE BRIEFED ABOUT WINDSHEAR AND WENT OVER THE RECOVERY PROC. ONLY SOME VERY LIGHT TURB DURING THE APCH; BUT THE FLT ATTENDANTS HAD BEEN SEATED EARLY. ON THE DOWNWIND VECTOR FOR RWY 26; WE NOTICED A HVY SHOWER INSIDE THE MARKER. ON BASE LEG IT SEEMED LIKE IT HAD MOVED CLOSER TO THE FIELD; BUT HAD GOTTEN STRONGER. ACFT WERE STILL LNDG THROUGH IT; BUT WE DISCUSSED THAT WE WOULD MOST LIKELY BREAK OFF THE APCH. ON FINAL AFTER INTERCEPTING THE GS; WE WERE IN THE CLR JUST INSIDE FUZZZ; AIRSPD 170 KTS; FLAPS 20 DEGS WHEN THE NOSE PITCHED OVER AS THE AUTOPLT TRIED TO FOLLOW THE GS AND THE SPD STARTED TO RAPIDLY INCREASE. WE IMMEDIATELY EXECUTED THE WINDSHEAR PROFILE AND ENDED UP CLBING TO 12000 FT IN THE UPDRAFT. RPTED THE INCIDENT IMMEDIATELY TO ATC AND DISPATCH AS SOON AS ABLE. EXCEEDED THE FLAP SPDS DURING THE RECOVERY; MAINLY DURING THE INITIAL BIG INCREASE; BY ABOUT 10 KTS; AND MADE A LOGBOOK ENTRY. MY FO WAS A BIG HELP WITH CALLOUTS AND CHKLISTS AS WE DEALT WITH THE SHEAR AND SUBSEQUENT LNDG ON RWY 35L.