Only the Mk I Meteor was limited to 414 mph. The Meteor Mk III, which went into squadron service with 616 Squadron in December 1944, was capable of 480-490 mph.
The Mk I was really more of a serise of service development airframes than a actual fighter while the RAF waited for the more reliable Derwent I engines to replace the underpowered Wellands. If Rover hadn't kept dragging their heels and doing everything to go as slow as possible in 1941-1943, the British could of been flying the Meteor in 1943.
Rover took a practical working design, c@cked it up in an attempt to avoid patent and design fees, and put English jet production behind by almost 2 years. When Rols-Royce stepped in and took over developmen, it took them just 6 months to do what Rover had done in almost 3 years.
Rover had produced just 32 centrifugal flow and 6 axial flow engines by the end of 1942, and were bench testing at around 1,400 lbs. After Rolls-Royce took over engine production in January 1943, they produced 60 Welland engines in 5 months and were bench testing them at 1,500 lbs in March 1,600lbs by May adnd 1,700lbs in July. Rolls Royce produced around 170 Wellands in 9 months before moving to the more advanced and reliable Derwent.
Aviation enthusiasts wax lyrical about the possibilities of a LuftWaffe armed with Ar-230s and Me-262 in 1943. If Rolls-Royce had been in charge of jet production and developement, the Meteor could of been in regular squadron service by January 1944 and the Vampire/Spider-Crab possibly just a few months later. There was a 6 month delay in Vampire development brought about because the Halford engines were being suplied to the USAAF for the XP-80 project after they destroyed the first engine in ground testing.