INSTRUMENT RATED PRIVATE PLTS ON IFR PRACTICE FLT DEVIATE FROM CLRNC AT WILL DUE TO WX AND TURBULENCE CONCERNS. ATC TAKES ISSUE WITH THEIR FAILURE TO OBTAIN CLRNCS PRIOR TO DEVIATIONS.

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THE INCIDENT BELOW DESCRIBES TO THE BEST OF KNOWLEDGE AN EXCHANGE BTWN ATC AND THE PLTS DURING A TRAINING IFR FLT. NO NEAR MISSES OCCURRED BUT ATC WAS ANNOYED AT PLT DECISIONS DURING ADVERSE WX CONDITIONS IN PARTIAL IMC. STANDARD WX BRIEFING INCLUDED AN AIRMET FOR TURB; ICING AND OBSCURATION. IFR CLRNC WAS VIA LVK1; V244 ECA DIRECT; MAINTAIN 4000 FT EXPECT 5000 FT IN 10 MINS; DEP FREQ 125.35. ATIS WAS 280 AT 6; VISIBILITY 10; CEILING 3500 FT SCATTERED; 4700 FT BROKEN; ALTIMETER 30.12. FSS RPTED POSSIBLE ICING BELOW FL180; AIRMET FOR TURB. REACHED ALTAM INTXN (LVK1 DEP) JUST BELOW CLOUD LAYER AT 4000 FT. ON TURNOUT TO ECA LARGE DARK CUMULUS CLOUD IN BUILD STAGE TOPS TO +7000 FT IN DIRECT PATH. OAT 36 DEGS F HIGH PROBABILITY OF ICING IN CLOUD. ATC WAS VERY BUSY ON RADIOS WITH OTHER TFC; PROBABLY TO DO WITH VECTORING AROUND WX CLOSE TO THE LIVERMORE HILLS. TO AVOID CLOUD AND HVY POSSIBILITY OF ICING TURNED SE TOWARDS TRACY ARPT. TEMP 35 DEGS F. TRACY COULD SERVE AS AN ALTERNATE ARPT TO LAND IF NECESSARY AND IS THE MISSED FOR LVK. REACHED ATC 2-3 MINS AFTER TURN AT 4000 FT AND INFORMED ATC OF CHANGE FOR SAFETY AND THE ACFT IS NOT PERMITTED INTO ICING CONDITIONS. ATC WAS VERY ANNOYED AT THIS LATE NOTIFICATION; BUT WE DID CONTACT THEM AT FIRST OPPORTUNITY. ATC CLRED US TO ECA FOR PRACTICE ILS APCHS ONCE WE CLRED DANGER. ATC ASKED US IF WE WANTED TO CLB TO 5000 FT OR STAY AT 4000 FT. WE INFORMED ATC WE WOULD CLB TO 5000 FT. WE THOUGHT WE COULD CLR ANOTHER SMALL CELL AT 5000 FT. CLBED TO 5100 FT IN MODERATE TURB. ALT IN AUTOPLT +/-150 FT DUE TO TURB. ON WAY TO ECA IT BECAME APPARENT WE COULD NOT CLR THE CLOUD SO WE STARTED A DSCNT TO 4000 FT. WE BELIEVE ATC WAS BUSY AND WE INFORMED THEM AS SOON AS THE AIRPLANE WAS OUT OF TURB AND ATC WAS NOT BUSY. THIS TOOK PLACE AT 4300-4500 FT AGL. ATC INFORMED US THAT WE WERE FLYING AT 3500 FT. WE HAD 2 PLTS AND 4 INSTS CAPABLE OF PROVIDING ALT AND ALL SAID WE NEVER DSNDED BELOW 4000 FT; OUR INITIAL ALT. THE CTLR WAS VERY AGITATED WITH US AND WE BELIEVE HE HAD SIMILAR EXPERIENCE WITH OTHER PLTS AND HIS HVY WORKLOAD. WE WENT ON TO FLY 4 PERFECT ILS AND VOR APCHS WITHOUT INCIDENT IN VFR CONDITIONS. ATC TOLD US TO LAND AND CALL THE CTR FOR PLTDEV AND WE COMPLIED. WE BELIEVE THE PIC HAS THE ABILITY TO CHANGE ATC INSTRUCTIONS IF IT IS BELIEVED THE SAFETY OF THE FLT IS IN DANGER; WHICH WE DID. THE ATC CTLR WAS UNAWARE OF THE FLT CONDITIONS IN THAT PARTICULAR AREA OF FLT AND WAS IN OVERLOAD CONDITIONS WITH OTHER FLTS. WE WENT ON TO CONTACT 4 PERFECT APCHS WITH ANOTHER CTLR. WE CONTACTED ATC WHEN WE WERE CAPABLE AND WHEN WE WOULD NOT STEP OVER OTHER XMISSIONS. ATC SHOULD HAVE DECREASED HIS WORKLOAD OR ASKED FOR ASSISTANCE DURING THIS SIT. THE CTLR WAS AGGRAVATED DURING THE FLT AND ANOTHER PLT COMMENTED THAT HE (ATC) WAS DOING FINE. APPARENTLY DUE TO ANOTHER FLT SIT.