As exhausts go, the power gains are from deleting catalytic converters. The gains are in the low to mid end of RPM.
Sound is mostly form the muffler/axel back of your choice, some even go without mufflers.
Deleting the resonator will add that burble/grumble at shift points.
The European airbox can be cut at the indent for the headlight access to gain more sound, colder air and perhaps some power. Its will resemble the current AFE magnum intake for our cars. the 130i guys have tested this with dyno's.
So get a 2" or 3" circular rubber plug form a home hardware type store, drill with the appropriate hole maker attachment and experiment. Plug it up if you dont like.
The euro box also accepts euro K&N drop in filter which is the oiled version of the one the euro BMW Performance airbox uses. AFE offers both oil and dry versions. Both available online( amazon, ebay and other) for substantial discounts over official K&N and AFE websites.
128i Sport 6MT converted to Euro 130i spec, tuned by evolve ~220 whp 207 wtq(ft-lb) SAE
In-progress: n54 ssk, m3 trans mnt, e36M lip Wishlist: m3 susp, n55 eng mnt, headers, LSD, finn dif e60
"The 1-series is the last car that BMW engineered before the Germans, as a car-making culture, fell out of love with driving." - R&T 2013 135is