That "within a few seconds" part is important because it kills the entire "impossible speed" theory with a little common sense.
within a few seconds we had exceeded the maximum operating Indicated Air Speed of 360Knots/h (415mph); then the needle continued to rise until it hit the stop on the indicator at over 400Knots/h (460mph). At this very fast speed you only have the Mach indication to go off, as IAS (Indicated Air Speed) is off the scale. The aircraft continued to increase speed until it reached .86 Mach (654mph), which is its rated airframe Mach speed limit. This makes complete sense, as the manufacturer does not want you to exceed this but wants you to have the maximum thrust available in case of emergency. At this air speed I was surprised at how easy it was to maintain my attitude once the aircraft was trimmed.