Spitfire: the History has MA766 as a Merlin 63 aircraft.
There's more info on 150 octane usage at
http://pub131.ezboard.com/fallboutwarfarefrm31.showMessage?topicID=535.topicSee also the links on page 2 of that thread.
As a sum up, all the Spit IXs in ADGB were using 150 octane from Spring 44, most of the rest of ADGB soon followed (Mossies etc). In July 44, Britain produced 40,000 tons of 150 octane, ADGB used 12,000 tons. ADGB usage fell off as the Germans retreated from France and Belgium.
2nd TAF switched to 150 octane in Jan 45. US 8th AF switched in the summer of 44, for all it's fighters. Mustangs at least switched back to 100/130 towards the end of the war.
In the RR documents on one of the links, it gives details for which engines can and can't benefit from 150 octane. The Merlin 61 isn't listed.
The description for the Merlin 63 (and a few others) is "These engines are a development of the Merlin 61 type, and are essentially high altitude engines. They have a strengthened supercharger drive which was introduced to permit the use of 21lbs boost pressure, and which is likely to be the main limitation to futher increases in boost pressure."
The Merlin 63 is listed as 18lbs on 100/130 ful, 21lbs on 100/150.
I don't think the Merlin 61 ever used more than 15lbs operationally, and that was probably down to the supercharger.
Note, on the link Funked posted, the Spit IX on 150 octane was performing poorly, about 20 mph slower on 18lbs boost than was usual for a Spit IX. Go to the Spit VIII page for a better idea of what a Spit IX on 150 octane should be capable of.