As far as the horsepower output of the next RL, I think 300hp is a good guess. When we look at the current Honda/Acura sedan lineup, the trend is in the following:

Honda Civic EX: 127hp
Honda Accord DX/LX/EX: 160hp (+33hp from Civic EX)
Acura TSX: 200hp (+40hp from Accord 4 cylinders)
Honda Accord LX-V6/EX-V6: 240hp (+40hp from TSX)
Acura TL: 270hp (+30hp from Accord V6)


So If we add 30hp to the TL, the horsepower of the next RL is 300hp.