Here are the official summaries on the 150 octaine fuel with the USAAF and RAF.
http://www.wwiiaircraftperformance.org/150grade/150-grade-fuel.htmlInto Service with the Royal Air Force
Following successful testing, the Spitfire IX's Merlin 66 was cleared in March 1944 to use +25 lbs, obtainable with 150 grade fuel. 29 In early May, No. 1 and No. 165 Squadrons comprising the Predannack Wing, were the first to convert their Spitfires to +25 lbs boost and employ 150 grade fuel on operations. Air Defense Great Britain (A.D.G.B.) shared a report, dated 16th June 1944 with A.E.A.F. summarizing the RAF's experience with using 150 Grade Fuel in Merlin 66 engines. All pilots reported most favorably on the value of the high boost pressures obtainable with 150 Grade Fuel, however, Technical Staff felt that before the fuel was introduced on a large scale that the causes of backfires must be established and that at least 12 engines should complete 200 hours each. 30 Eventually the backfire problem was sorted out, see: Backfire trouble resulting from use of 150 grade fuel. 27 July, 1944 and Backfire trouble resulting from use of 150 grade fuel. 12 August, 1944 31, 32
The increased performance obtained with 150 Grade Fuel was put to good use by Mustangs, Tempests and Spitfires in intercepting Buzz Bombs launched against Britain beginning mid June. Performance increases at sea level were as follows:
------------------------------130 Grade---- 150 Grade
Spitfire IX --------------------335 mph----- 358 mph +25 lb
Spitfire XIV ------------------359 mph------ 366 mph +21 lb
Tempest V -------------------372 mph------ 386 mph +11 lb
Mustang III (V-1650-3) -----360 mph------ 390 mph +25 lb