Realize that the ECU upgrade, Intake change and exhause system all work together. Short of taking the motor apart to change valve sizes, camshafts and and pistons, you are limited in what you can improve and how much that improvement will be.
An air intake system that breathes easier, should allow you to get air into the motor somewhat easier. A non-restricted exhaust, will allow you to get rid of exhaust easier. But without an ECU re-flash, you likely won't notice much. The ECU controls the fuel/air mixture. This is vital since, to make power, you need, Air, Fuel and Spark. Most ECU upgrades are a "rob peter to pay paul" scenario. You might gain HP in the upper RPM ranges and sacrifice some low end torque to get it.
To do all three would be the "right" way (intake, ECU and Exhaust which, hen combined could give you 10% more power (or whatever the "claim" may be)). 10% of 245 is 24.5 giving you approx 270hp. From a validation standpoint, it mich be worth the $$ to have the car dyno'd after each stage to see how each change improves performance and then have the overall numbers as well.
Just remember to replace the exhaust before your state emmisions are due. I would also think (just a guess here) that the OBDII system would notice the changed exhaust (no cats/no O2 sensors in place). I would also believe it illegal for any shop, nowadays, to install parts that are purely "race only" in nature on a street registered vehicle. Not sure how much the dealer appreciates that, from a warranty perspective, on a leased vehicle