The way I look at it the K24 is in no way superior to an R18. The gear box can only handle about 300 wheel torque. The engine is pretty much a high compression economy motor with variants making as little as 160hp.
2012 Si coupe is 2,887lbs
2012 EX coupe is 2,680lbs
IMO my R18 at 12psi with a 50 trim turbo weighing in under 2,600lbs after weight reduction, is pretty damn quick I've beaten many 335i's, Si's of all trims with/without mods, Challengers, WRX's, V6 accords, Range rovers, you name it whatever car is considered "Sporty" the performance is pretty much on par. It's also way more entertaining when you pull up to a stop light after, and they just stare at you demanding what type of got dang engine that thang got.
K24 you have to build it
R18 you have to build it
Just a turbo kit with supporting mods for an Si you're in over 7k without a tune. My custom kit with tuning, supporting mods, and some custom one off fabricated parts that no one else in the world has came in at $5,200.
If anyone is looking into a turbo R18 Greddy teamed up with RevHard and made a bolt on kit for 9th gen R18's. It still says TBA but I've seen come up for sale for around $4,200 for the complete kit.