I am curious if you also got some of NVH from your diff after above mods? I "just" have powerflex subframe inserts and diff poly bushings, and my quaife diff starts to produce clicking noises as soon as I engage D, and then there's a whine depending on speed. It is especially loud around 140-160km/h.I had the same concerns when I first got my 2010 e90 335 LCI M Sport in 2013. Going fast around sweepers and corners were never confidence inspiring. It didn't help at all it had an open diff and spun the inside wheel. The car had a ton of under-steer from the factory, and for some people it's a safety thing, but for us driving enthusiasts, can be down right frustrating.
What I did to dial it in was I went with Ohlins's DFV Road and Track coil-over suspension to set the ride height along with it's excellent valving (Coming from the Sport Bike/MotoGP world, Ohlins is the creme de la creme. I lowered my lap times and increased my cornering confidence at the tracks with my Ducati Race bike, so I went with what I was familiar with ymmv), M3 control arms and guide rods for front and rear to enhance traction when cornering (along with e90 m3 alignment specs, had to slot the shocks for more negative camber) , installed ECS's rear trailing arms along with Whiteline's RTAB polyurethane bushings for more grip and less deflection, installed m3 sway bars from Eibach on front and rear to reduce side to side weight transfer (rear sub-frame was going to be lowered so I might as well, I'm too lazy to do the job twice), went with Turner Motorsport's Aluminum Sub-frame Bushings to reduce rear sub-frame deflection that causes that confidence killing floaty/disconnected feeling when increasing speed mid corner, esp hitting a bump, replaced the differential bushings with MFactory's solid diff bushings(since the diff was coming out anyways), dropped the rear open diff pumpkin and replaced it with a fully re-built MFactory 3.46 LSD, and called a tow truck to tow it to an alignment shop to get my specs on the car. Took me the entire day including cussing breaks and lost time from recharging dead impact wrench batteries (ran out of juice removing the sub frame bushings using my special tools).
The car is a whole new beast. I had to re-learn it all over again as I fell in love with it all over again lol.
It handles really well and just wants to go faster around corners. It feels really connected to the road and provides the feedback you need. There isn't a slop on the rear end, it stays nice and tight. When entering an S turn or chicane, the side to side weight transfer roll is significantly reduced. In corners, you can feel the outside wheel driving the car forward as corner speed increases. On corner exit, you have to completely relearn the car as it wants to drift if you get greedy on the throttle, the back-end just wants to step out, but its a predictable type of feeling, you steer with the gas pedal and be quick to counter-steer with the hands, etc. in the event the rear steps out to just be smooth with the throttle.
Why did I add these parts in one project? Well because for one, I don't like doing the job twice and I see the opportunity to install things while the opportunity is there, and two, I severely disliked how my car sucked going around corners. The diff was coming out and so was the rear sub-frame, I might as well install the parts while they are both out. for example, if you plan on installing sway bars for the rear, the rear sub-frame needs to be lowered, if that's the case, you might as well do the rear sub-frame bushings, vice versa. I have the QuickJack so it made the project a whole lot easier. As far as for NVH (Noise, Vibration, and Harshness) it's a tad a bit more on driver feedback (a good thing), but on smooth roads, hardly can feel a thing. I do a lot of canyon carving in the twisties as I find joy in it more than going fast in a straight line, it's also my daily driver as well. I didn't go with a diff lock-down brace, I'm having no issues with wheel hop when launching and I dislike how some of it covers the rear diff drain bolt since I swap fluids every 15k miles.
I know it's a long post but I hope this helps.