A319 FLT CREW IS INSTRUCTED TO MAINTAIN 170 TO THE 4R MARKER AT BOS WITH 60 KT TAILWIND ALOFT AND SLIGHT HEADWIND BELOW. AUTOPLT IS UNABLE TO COPE AS IAS INCREASES; GROUND SPEED DECREASES. A GAR IS INITIATED AND SECOND ATTEMPT IS SUCCESSFUL.

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AFTER A LONG AND TIRING DAY IN ALMOST CONSTANT TURB; ON A CAT III APCH TO RWY 4R AT BOS; WE HAD A 60 KT TAILWIND TO THE OM. BELOW THAT; THE WINDS DIMINISHED TO 090 DEGS AT 9 KTS. APCH TOLD US TO KEEP 170 KTS TO THE MARKER. AWARE OF THE TAILWIND; WE SLOWED UP AND CONFIGURED EARLY. WE LOWERED GEAR AND CONFIGN 3 DEGS FLAPS; SAVING FULL FLAPS (MAX SPD 170 KTS) UNTIL 4 MI FROM THE OM. WHEN I SELECTED MANAGED SPD THE ACFT WAS UNABLE TO SLOW UP BECAUSE OF THE TAILWIND. TRIED SOME SPD BRAKES AND WAS ABLE TO GET IT SLOWED UP BELOW FULL FLAPS SPD. WHEN I LOWERED THE FLAPS; THE ACFT 'BALLOONED' UP. IN ORDER TO CAPTURE THE GS; WHICH WAS NOW WAY BELOW US; THE AUTOPLT GAVE US A SIGNIFICANT NOSE DOWN ATTITUDE. I DECLARED 'UNSTABLE' AND BEFORE COMMANDING TOGA REALIZED THAT AN ABRUPT ACCELERATION WITH THE NOSE POINTED DOWN WAS NOT IN OUR BEST INTEREST; SO I DISENGAGED THE AUTOPLT AND PULLED THE NOSE UP. I THEN COMMANDED TOGA. AFTER OUR GAR; I TOLD APCH CTL THAT FOR OUR NEXT APCH THAT WE WOULD NEED 150 KTS TO THE MARKER AND THAT THEY NEEDED TO GIVE US LONGER SEPARATION BEHIND US. THE NEXT APCH WORKED OUT MUCH BETTER ALTHOUGH IT ALMOST BECAME MY FIRST CAT IIIB APCH WITH NO VISIBLE REF TO THE RWY. THE FOG WENT ALMOST DOWN TO THE DECK. WITH TAILWINDS LIKE WE EXPERIENCED; BOS APCH SET THIS GAR UP BY MANDATING 170 KTS TO THE MARKER. THIS HAPPENED ONE OTHER TIME TO ME IN BOS ON ANOTHER ACFT. THE PRESSURE TO KEEP UP THE LNDGS/PER HR STATISTICS SHOULD BE SET ASIDE UNDER THESE CONDITIONS.