AN ACR LTT CAPT REGRETS HAVING ACCEPTED VISUAL SEPARATION FROM A CLBING ACR LGT.

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DURING CRUISE SWBOUND ON V39; ATC CALLED TFC AT ABOUT 10:30-11 O'CLOCK POS AND 10-12 MI. I SIGHTED THE TFC; WHICH WAS 2000-3000 FT BELOW ME; AND WAS INSTRUCTED TO MAINTAIN VISUAL SEPARATION WHILE THE TFC CLBED THROUGH MY ALT. I WAS SWBOUND; TFC WAS NWBOUND. BASED ON PRIOR EXPERIENCE; I EXPECTED THE TFC; AN AIRBUS; TO PULL AHEAD AND CLB ABOVE ME PRIOR TO OUR PATHS XING. AS I KEPT THE TFC IN SIGHT; IT DID INITIALLY SEEM TO BE ACCELERATING AHEAD OF ME; BUT CONTINUED OBSERVATION INDICATED THAT IT WAS NOT BY MUCH. CONSEQUENTLY; I BEGAN A GENTLE TURN TO THE R TO OPEN THE POINT OF INTXN. AS THE TFC CONTINUED TO CLOSE AND CLB; IT BECAME OBVIOUS THAT WE WOULD PASS VERY CLOSE; AND I COMMENCED A TURN TO THE L TO PASS BEHIND THE TFC; WITH A VERY HIGH CLOSURE. AT THIS POINT; I ALSO BEGAN TO CLB. AS THE TFC PASSED DIRECTLY BENEATH AT ABOUT 1000 FT HE RPTED THAT HE HAD STOPPED HIS CLB. HE ALSO APPEARS TO HAVE BEEN IN A R TURN; THUS WE HAD EACH TURNED INTO THE OTHER. I BELIEVE THAT THE POTENTIAL FOR A COLLISION WAS VERY HIGH -- THIS IN SPITE OF THE FACT THAT I HAD CONTINUOUS; UNBROKEN VISUAL CONTACT FROM START TO FINISH. I FOUND IT VERY DIFFICULT TO JUDGE THE RELATIVE MOTION OF THE OTHER ACFT WHILE IT WAS CLBING AND CLOSING SIMULTANEOUSLY. I ALSO FOUND THAT; SINCE I WAS IN CRUISE ALONG AN AIRWAY AND THE OTHER ACFT WAS 'MANEUVERING;' I WAS RELUCTANT TO MAKE DRAMATIC CHANGES IN HDG; A RELUCTANCE THAT WAS FED BY MY EXPECTATION THAT THE JET WOULD PULL OUT AHEAD AND ABOVE. FURTHER; BY THE TIME IT BECAME OBVIOUS TO ME THAT MY EXPECTATIONS WERE NOT BEARING OUT; OUR 2 ACFT WERE QUITE CLOSE; AND CLOSING FAST. THE SIT DEVELOPED VERY RAPIDLY IN ITS LATTER STAGES. SOME OBSERVATIONS SUGGESTIONS: 1) THE CTLR SHOULD HAVE BEEN ABLE TO SEE THAT OUR ACFT WERE ON COLLISION COURSES; OR CLOSE TO IT; AND THUS SHOULD NOT HAVE ISSUED VISUAL SEPARATION INSTRUCTIONS. 2) LACKING AN OBVIOUS AND DRAMATIC BEARING CHANGE; I SHOULD NOT HAVE ACCEPTED VISUAL SEPARATION RESPONSIBILITY. 3) WHEN VISUAL SEPARATION IS USED BTWN AN ACFT IN CRUISE AND ONE THAT IS 'MANEUVERING;' IT SHOULD BE THE 'MANEUVERING' ACFT THAT MAINTAINS SEPARATION. IN THIS CASE; WE BOTH WERE MANEUVERING AT THE END; AND EVIDENTLY AT CROSS PURPOSES. IN THE FUTURE; I WILL NOT ACCEPT VISUAL SEPARATION WHEN THE ABOVE CRITERIA ARE NOT MET. IN RETROSPECT; IT WOULD HAVE REQUIRED AN ALMOST IMMEDIATE 45 DEG HDG CHANGE ON MY PART TO MAINTAIN COMFORTABLE LATERAL SEPARATION.