BASF tape formulas

DIN Type II Reference Tape C 401 R BASF 100% pure chrome
IEC Type II Reference Tape S 4592A BASF 100% pure chrome
IEC Type II Reference Tape U 564 W (replaced S 4592 A in October, 1987, in the IEC meeting in Prague)

Magnetic Media Information Services, Volume XIII, No. 5 (August 20, 1993) discusses the technical work of Dr. Manfred Ohlinger, BASF's chief of pigment development. Dr. Ohlinger discussed work on CK60/XH, a chrome pigment with a coercivity beyond 1000 oersteds. He had already produce CK/75/230X with a value of 900 oe. and CK57/200X with a value of 670 oe. BASF was in full development of advanced pure chrome pigments for new 3480 cartridges and other media. 

BASF had been producing pure chromium dioxide pigments in a huge reactor in Ludwigshaven, Germany, since the late 1960s. In 1995 the oxide lineup included:
CK 40-14 for audio tape
CN 43-11 for high performance, single-coat audio tapes
CK 37-11 for the lower coating of high performance chrome audio tapes. This pigment was designed for non-cross-linked binders.
CK 48-21 was for the upper layer in cross-linked dispersions. These oxides were used in Chrome Super and Chrome Maxima tapes. The tapes were identical and differed only in the housing and the tighter specs for Chrome Maxima. Most Chrome Super performed exactly the same as Chrome Maxima. 

CK 50-21 was pure chrome used in VHS, S-VHS, TMD, and DCC formulations. (BASF made the only DCC tape. It was the tape in TDK and every other DCC cassette made.)

There were CC variations of these pigments. They differed in that oxygen molecules were attached to the crystal surface to prevent degradation to hexavalent chrome in the presence of water. 

BASF used 100% pure chrome formulations for its EE reel-to-reel tape and for Loop Bin Master 920 and 921 used in the duplication industry before digital bins arrived. The only "hybrid" chrome/cobalt audio formulations appeared with the introduction in 1993/94 of "Chrome Plus" duplicator tape that had a small percentage of cobalt-ferric pigment added to raise AT315/MOL315. Its AT315 was 2-3 dB better than competing chrome tapes. Chrome Plus was also used in Chrome Extra audio cassettes from that point forward. 

In 1992 world-wide production of magnetic powder by weight was 11% for chromium dioxide, 55% for co-fe, 32% for standard ferric, and 2% for metal powder. This total includes all applications: audio, video, computer data.

In 1994 BASF used a high-performance plastic that could withstand 95 degrees C. (203 degrees F.) without deformation. This plastic was used in the sonically welded Reference Maxima series. The tape was BASF ferric-cobalt because the heat resistance of the plastic would be wasted on a tape that had a much lower Curie point. (It was chrome's low Curie point that made it the only choice for thermal duplication--TMD--that was used for high-speed video tape duplication.) BASF kept Chrome Maxima and Chrome Super in the cassette lineup as 100% pure chromium dioxide tapes and the 85/15 Chrome Extra as its first and only hybrid chrome audio tape. 

As for "audiophile" opinions, I remember reading a discussion in The Absolute Sound condemning the process. It was obvious that the writer, an editor at the magazine, had little idea of magnetic recording. If you want an audiophile journalist's perspective on high-speed duplication, you would have to turn to John Borwick or Angus MacKenzie's work in British publications.