The Russians are looking at advanced high speed helicopter concepts too (Paid Subscription Required):

Among the concepts are:

• The Mi-X1, a 5 ton class aircraft with a top speed of around 450-500 km/h.
• The Kamov Ka-92 which uses a coaxial rotor with retreating blades offloaded, much like Sikorsky’s X2 demonstrator.
• The Ka-90, which has a rotor which folds down along the fuselage for high speed (700 km/h) flight.