Brakes:
Lets talk brakes. So with the swap I spent some time talking with Ed from BimmerBum who was very helpful with informing of what choice to make!
Front choices: - 286mm vented (e36 325/328) - Wheels: 15"
- 300mm vented (z3 3.0i/e46 325) - Wheels: 16" BUT possible 15" with 5 series offset ** (more on second post).
- 315mm vented (e36 m3)* - Wheels: 17" BUT 16" with 5 series offset, like et20 or lower!
- 325mm vented (e46 330)* - Wheels: 17"
* e46 330 vs m3
- 330: has larger rotors 325mm (330) vs 315mm (m3)
- m3: has thicker rotors, directional venting, caliper piston is larger than 330 for more clamping force. Also with the 315mm rotors you can find two piece euro ones which are also a lot lighter.
** 300mm rotors with 15" wheels. A member gave me pictures so I need to find them and post them, but I think in the same way that 16" wheels fit over the 315mm m3 rotors with low offset, usually comes stock with e34 wheels, lower offset will actually allow for 15" wheels to barely fit on 300mm rotors. He has 15x8 et23? (e30m3 specs) wheels over stock front z3 3.0i brakes which are also 300mm
Rear choices: - 272mm Solid rotor is basically it. But we have some bolt on caliper choices that have larger diameter caliper piston diameters:
- Smallest to largest: stock (??mm) --> z3 6cylinder (37mm?) ---> e34 (38mm or 40mm not sure which is which)
- SRS Concept has come up with an adapter that allows for 300mm rotors from the 1-series to be fitted with e46 rear 325 calipers--> 40mm piston, which seems like a great fit with 315mm m3 fronts and stock e36 m3 brake booster. I have NOT personally tried this so its just a guess.
Then comes the question of what is actually needed?? I don't want to add to much weight with large brakes that are heavy and not needed or limit my wheel choice. Its all about balance!
The z3 3.0i came from the factory with 300mm fronts and same as stock rotor but the 6-cylinder caliper piston is larger allowing for more clamp force. The z3 3.0i is roughly 2950lbs, has 225hp. It seems like that is exactly where my swapped 318ti is at. ~2900lbs around 220hp (m52 w/s52 cams) so I decided to go forward with that setup.
Result: Front: 300mm Zimmerman blank rotors with calipers (Surprised when I compared the piston size of the calipers that they were exactly the same.)
Rear: Stock rotor z3 2.8l calipers
Pads: Hawk HP+
Misc: Super Blue fluid, SS lines all around.
Pictures: 
Solid 286mm vs 300mm:
Front Bolted on:
Rear Bolted on:
Comparison of old 318ti piston size vs z3 6cylinder - Piston is a bit larger as shown in the second picture:
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Results: At first I was hesitant using Hawk HP+ pads on a street car, due to the brake dust and brake noise that others have mentioned. Hawk gave instructions to brake them in by 7-8 hard stops at moderate speed, then another 7-8 hard stops at higher speed. It is important to let them heat up and bed properly to the rotor, so your not supposed to come to a complete stop and also let the brakes cool down completely after the bedding process. I ended up finishing the install around 11:30pm, put all the tools away, cleaned up, showered, by then it was close to 12:30am, so the roads should be quiet. Went out did roughly ten 50~60mph hard braking (without locking up) to 10mph before speeding up again to repeat, then did approximately four stops at 70~75mph. The brakes also put on a bit of a spark show, and by that time they started to fade a little already. So I just continued into the canyon to let the brakes cool. It was interesting that after 20min of coasting/cruising, the front was cool to the touch, but the rear still felt hot. It seems like the rear could use vented rotors. I used a lot of the anti-squeak lube to try to minimize noise but now its been a few days and they are definitely are starting to squeak. Its not too bad though, it is mostly at low speeds that it will squeak a little. Also this setup is good enough to get my crappy 500 or something thread wear Falkens 225/45/17 to lock up in the front (road was uphill, so more weight in the rear, and the road was a bit rough). I would be very interested to try some softer summer tires and see how well it can brake. Cold braking also has not been a problem.
The new setup in comparison to the old setup is noticeably better! I am definitely happy with this setup and will see how much life I get out of it, it gives me much more confidence even when going downhill at like 70mph, I can feel the pads actually digging into the rotors and slowing down the car, the bias also seems well spread between the front and rear. Other then maybe a little better heat dissipation in the rear, I am very happy with this setup.
Also went for a drive with my housemate on Angeles Crest Highway Saturday.
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Update: the HP+ pads get really squeaky, like annoyingly so. Not recommended for the street.