On the coupe i think the fronts are 235x45x18 and the rear is 265x40x18. This is from memory.
Given the engine was in front I always had the fronts pumped higher than the rear... in the region of 32 fronts and 30 rear. All this is subjective given what type of ride I was looking for. Road condition and temperature played a big part in my decision making.
U mentioned 29psi for all tires. That sounds a bit low to me. Check the conversion again what does it say exactly on the sticker. I always found that the factory recommendation too high for my liking.
The factory recommendation for the GS is around 36psi. For me, thats way too high. I have got my tires around 33-34psi all round.
I got them the same psi all round this time coz the way I drive the GS, I find that the rear sags and rolls too much when hard cornering.
I also use Nitrogen in all 4 tires. Given the variation of temperature in Singapore between night and day, using N gives me consistancy. They feel exactly the same on a 36 degree hot day and 25degree morning. Mind u this is air temp that I am talking about. The road temp is probably around 50degrees.
I think one of the best ways I learned about my car was to try different pressures and see which best suited my driving style and road situation. There is no real right or wrong. The recommended numbers is just a starting point.