Thanks, but I love my G70, and if both of these were on the market and I had to make a decision today, I'd still go with the G70. Acura always gets tech right though, so the tech will be ahead, at least until the 2022.
I had the pleasure of enjoying a C63s for a week. While not comparable in terms of performance, that interior is horrid. The rattles and creaks. Yuk.I haven’t driven all of these cars. Without regard to only HP/torque/0-60 times, here are some sentence fragments for your reading pleasure (or displeasure):
Kia Stinger: Bloated G70. Suspension too soft. Interior is OK, but quality of materials is subpar.
M340i: Ooh, silky smooth straight 6. Huge power. Flat cornering, but ride is less comfortable. Great technology but, in typical BMW fashion, over engineered. Styling isn’t for everyone. Seats are great.
S4/S5: Sedan styling just OK, but coupe is elegant. Luxurious interior, but may not age well. AWD system isn’t as rear biased as BMW. Infotainment is love it or hate it. V6 sounds good, but lots of turbo lag and poor throttle mapping.
CT5-V: Big improvement over prior Cadillacs, but that’s not saying much. Interior quality is catching up, but still not there. Transmission tuning is behind others. Questionable reliability.
TLX Type S: Basically, an expensive Honda. Improvement in styling over recent Acuras, but still a bit polarizing. Unimpeachable reliability.
C43 AMG: Some love the styling, others hate it. Very sporty suspension and exhaust, which might get tiresome after a while. Interior styling is beautiful, but material quality is lacking in some areas. Too much alcantara.