Pardon me if this has been posted before. I just came across the 335is, a limited model slotted in between the 335i and M3. Seems to me similar in concept to the ZHP. Any have any experience with one? I may have to add it to my list.

From Wikipedia:

335is (2011–2013)

The 335is was produced in coupé and convertible models for the North American market. It sat between the regular 335i and the M3 in the model line-up, and approximately 6,300 units were produced. The 335is uses a higher performance version (N54T) of the N54 engine from the 2006-2013 335i, which increases boost from 8.7 to 11.6 PSI. This results in 320 horsepower and 332 lb-ft of torque, plus an overboost function raises torque to 370 lb-ft for up to 7 seconds.

The 335is has stiffer engine mounts and an upgraded cooling system, with a heavy-duty radiator fan and two heat exchangers, one an engine oil cooler, the other a secondary coolant radiator. To accommodate these heat exchangers, which are located ahead of each front wheel, the 335is has larger air openings, similar to the M3. Fog lights were removed from the coupé version to allow for the openings, although they remain on the convertible version. In addition, the 335is is equipped with a revised, high-flow exhaust system, with the twin exhaust pipes finished in matte black, and a rear bumper that incorporates a diffuser-style piece.

Transmission options were a 7-speed double clutch transmission (DCT) with launch control (Same DCT transmission as the M3 but with different software programming) or a 6-speed manual transmission controlled by a short-throw "M" stick. The manual transmission has a heavy-duty clutch with more holding power than the regular 335i.

Interior upgrades include a thicker, "M" steering wheel, "M" steel pedals, standard sport seats, "M" door sills, and textured aluminium trim with "335is" badging on dash and in instrument cluster. Exterior differences are black kidney grills, and "Style 313" split-five spoke "M" wheels in 18-inch or 19-inch size, standard Shadowline window trim (instead of chrome), gloss-black side mirrors (instead of body colored mirrors).