An ex-Lightning mate of mine transferred to the VC10 in 1973. He said that, if necessary (VIP trips) it would cruise at M0.94.
Not many jets of that era or this could achieve that.
The VC10 being one of them. M0.94 is, I'm sorry to say, WIWOL exaggeration (as in 'AI 23 picked up targets at over 10 miles')....
Cruising at an indicated M0.91 was outside the release to service limits, but very probably just about possible in a very highly polished VIP jet - fuel consumption would have been horrendous though. I've certainly cruised the Pond at M0.88 indicated, but the only time I took the RAF VC10 over M0.9 was during properly authorised post-maintenance air tests.
I suspect that the Convair 990 'Coronado' was quicker than the VC10, but probably didn't have the fuel to cruise at high IMN for very far.