Whilst the Lynx isn't much good hot and high (better with T800 engines) it is still the world speed record holder - 216Kts (249 mph) set in 1986
Yes G-LYNX was modified but not by much - the military release to service for Mk 7 (no TOW booms) and 9 had a VNE of 156 Kts which was very achievable in level flight and could easily be exceeded if you weren't paying attention.
A light slick (no TOW booms) could sustain 3000 f/min RoC