Regarding the hesitation on sudden flooring or power demand, it seems to be a very annoying BMW peculiarity. Don't get it in my Toyota but even my mighty N54 had it before the tune, with tune I'm not smiling; rather giggling like a silly young girl when the foot goes to the carpet and rear lights up.
. But yes I did have that in the E46 330 too and even the prior E46 M3 I had. The M3 though was an SMG and it would buck then literally catapult ahead. Talking of coolaide, that damn car with the SMG was just awful. I traded it for a new 330 step tonic never looked back. I couldn't drive it smoothly in the pothole infested NYC environs I lived in at the time. Power was on off affair where it was always too little or too much.
Dealer couldn't understand my wanting to dump it for a 330ci. I test drove one and ordered one same day and dealer was just dumbfounded. So I can understand your wanting the 28i over the 35i, but for me no argument here I'd go with the 35i and yes drove both. By the way when you really step on that N20 it is noisy in a strained kinda way compared to the relaxed N55. I don't really care for a tune on the SAV though, I'll leave that to the car.
I don't particularly like the looks of the X3 but can live with the M-Sport. But it's leagues better than the the older model it replaced. I picked the Toyota RAV4 over the older model that it thoroughly spanked though few BMW fanboys will admit that.
Welcome, never mind our opinions go enjoy what you paid for is all, we will all have an opinion.