Just got the Michelin Lattitude Tour HPs - so much better than the Bridgestone Potenzas, much smoother and softer ride, particularly over road imperfections. Seem quieter as well. Makes the whole car so much better to drive. I would say that they match the comments the American RX owners are giving about them, so probably are exactly the same tyres sold here.
Came to £581 for four tyres including precision balance upgrade from F1 Autocentres (got 5% discount code from their Twitter account). One strange thing though - they couldn't do an alignment check as they couldn't find the RX400h on their system, and it wouldn't let them enter the data manually.