Item 1:
Underdrive pulleys reduce coolant flow, maybe not important if you drive a lot of short freeway, but long hot trips, or multiple short hard trips will stress the cooling system (water cooled Turbo bearings). Your choice though.
Item 2:
Some people are singularly unimpressed with the cat back exhaust systems available, but, as an owner I can tell you that my PTs performance AND mileage has gone up dramatically. Performance is subjective, so I can't do more than point to the verbage in the "Turbo Exhaust " post on this website, BUT mileage is hard numbers. Yesterday i just got back from an LA to Vegas and back: a 4000 ft altitude climb with lots of traffic, and my speeds were well over 100mph.... overall gas mileage: slightly more than 26mpg. My around town mileage increased also by about 5mpg. These numbers are mine, I only have a K&N drop in as mods to the engine, so you be the judge.
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