I also got about 10.3 km/l on that Sienna for at least 99% of highway mileages with only two passengers(I and my wife) and some light bulky stuff in the back.
I think my GSF should get a little better MPG which is 10.5-11 km/l. But, my GSF only accepts premium gas (95 or above)...
In my opinion, a little overdamped is not bad at all as a little overdamped may reduce a little grip but what you get is more immediate and confident handling...
Immediate and confident handling = FUN!!! (Of course, do not go TOO STIFF which is very bad...)
Today I changed ATF fluid for torque vectoring. So I have completely done the torque vectoring differential now which include differential fluid (center) and ATF fluid (right and left side).
I still have to do ATF fluid changes for the 8AT. (I need to do drain n' drop THREE times)
Some people think these fun luxury cars are too heavy... After I think about this for quite some time, now I conclude "I do NOT agree!!!"
Yes. These fun luxury cars are heavy. But, if you put some good stiffer suspensions like Ohlins DFV, they feel at least as nimble as stock Miata if not better.
I drove my GSF with Ohlins DFV 16/12K suspension about 8/10 for the last 6 months. For 8/10 driving I didn't feel its weight at all. For stock Miata I could feel its obvious weight transfer even though I just did 6/10 driving due to its much softer suspension!!!
I will also NOT do 10/10 driving on public roads in any time!!!
Why???
That's because public roads are very narrow compared with private closed race tracks which are very wide. There are also some novice or aggressive (and also dumb) drivers on public roads. Many things could also happen unexpectedly on public roads!!!
Today I also encountered an old Miata passing another car just before the other side of the corner at my lane. (I also encountered a stupid SUV did the same thing one month ago!!!) If I did 10/10 during cornering at that time, the result could be a disaster!!!
How about if I do 10/10 on race tracks in these heavy luxury cars???
Private race tracks are usually very WIDE. So if I do 10/10 on race tracks in these heavy and big cars, I do NOT think they will have any issues or disadvantage. (Of course, you still have to put some BIG tires on them)
I think why you think these heavy luxury cars are not good on mountain roads even with some suspension and tire upgrades...
That's because you try to do 10/10 on narrow public roads dangerously!!!
PS: I would say all the public roads are very NARROW if compared with private race tracks as you are supposed to drive your car on your own SMALL lane...
So I do NOT think I really need 400Z which is a lighter car... (I should buy Q50/Q60 instead)
Q50 or Q60 is a luxury car which have many kinds of luxury features besides quieter, better interior, more comfortable, better sound system, more practical (more seats and bigger trunk)...
If I like to increase fun factors for the car, I just need to put a stiffer suspension like Ohlins DFV. Then it would become more fun than what I really need...
Why I don't need a lighter car such as 400Z... That's because I don't do 10/10 driving or racing with other cars on public roads...