The Me 262 was rated for 540 mph. The RAE and US got well-maintained aircraft up to 525 - 529 mph after the war. The minimum acceptance criteria was 515 mph (ref Hans Fey). There was more like a 40 mph margin, at best.
The Me 262 Pilot's Handbook gives maximum level flight speed as 830 km/hr (515 mph).
Source: (1946) No. F-SU-1111-ND ME-262 A-1 Pilot's Handbook
This brings the speed differential down to practically zero, after other factors such as the Meteor's much superior acceleration and reliability are factored in.
Regards,
Magnon