I got 20% off the list price of my GS 300h Exec 18 months ago. I bought at the end of the sales quarter, so the dealer might have been aiming to reach his sales quota, and I took the zero mileage car off the showroom floor.
I find the 300h to be powerful enough. I usually drive in 'econ' mode, as I find the car an excellent long distance cruiser. If i want a bit more acceleration, say at a roundabout or junction, I switch to 'sport' which gives the car a more immediate response. The Exec model has smaller wheels and higher profile tyres than you will find on the other specs, which gives a slightly more comfortable ride, which is my preference.
I used Carwow to get prices from various dealers, then went to my local Lexus dealer as said can you match this else I'll go elsewhere. They matched the best price, plus about £600 more for taking the colour of the showroom car.
Since the GS is no longer going to be made you might find a very good deal.