You're going to get a lot of opinions on this topic but as someone who drives an 03 coupe with the bone stock DMF setup and also trying a 350z with a single mass flywheel your daily driveability will deteriorate. The banging and vibrations on a solid mass I drove in while pottering around in traffic drove me nuts. Also, going up steep grades at lower RPM's (such as following a slow car) you can feel the vibrations going through the entire driveline.

If you have no plans to track and you care about driveability go with the original setup. The original thesis with going to a SMF was because a DMF for our cars used to cost over $1000. No longer the case, our cars are getting older and prices have plummeted. A OEM dual mas LUK DMF067 has dropped in price dramatically and you can get it for $415 shipped from Amazon. Add an Exedy NSK1000 clutch for $250 plus 4-5 hours labour and you can get everything done for a bit over $1000. Relative to other cars in this class this is an incredible bargain to remain stock.

I have a single mass with an unsprung full face clutch (stock spec pressure plate) and have none of those problems that you're describing. There is less inertia for the initial launch but that's it, a little clutch chatter which I'm completely fine with but that's to be expected from any lightweight flywheel, revs VERY quickly.

My guess is the 350Z had a really low quality clutch or was maybe using a 6 puck or something that was WAY more clutch than needed (unless he was actually making 600whp) because those are really aggressive and add significant NVH.

Do your research, there's a lot of shitty clutches out there, but at the end of the day it all boils down to what you're building the vehicle for and how proficient you actually are at a manual transmission (yeah everyone thinks they're doing it right but a LOT of people aren't...)

Do you slam gears and pop the clutch a lot banging from one gear to the next? Stick with a sprung hub to save your driveline from early wear.

Do you regularly lug the engine a little on launch or hills (or launch at very low rpm)? Stick with the OEM dual mass flywheel because you're going to need the inertia to get moving (this includes folks who shift to the highest possible gear and cruise at city speeds in 5th gear around 1500rpm).

However if you don't mind the little extra noise from clutch chatter and keep the engine at a higher rpm where it naturally wants to sit (2500-3000 around town) then you will probably enjoy how much more free the engine feels by removing 15 lbs of rotating mass.

Always cracks me up when I watch people drive stick. Like..what are you doing. My dad taught me to drive clutch, basically the same way you just described and then one day I was driving my grandpa somewhere (he was an actual mechanic) and he was like "wtf are you doing?" Then he told me what I was doing wrong and I remembered at that point how often my dad used to be under his truck changing his clutch.

Anyhow, I'm in the same situation. At 171k miles, my original clutch is slipping slightly because of an emergency incident I had on a road trip. Got caught teetering on my tranny trying to take a turn onto a steep hill and had to burn my clutch dragging myself out. What an awful smell.

Is the JWT lightweight clutch no longer the happy medium for lightweight and driveability?

Not sure about the JWT, I know Z1 offers a "mid weight" single mass that's designed for folks who don't want the extra moving parts and hassle of a DMFW but also don't want as much chatter that a normal LWFW gives.

I think a lot of folks don't truly understand the differences between types of clutches and flywheels. Why they are designed the various different ways and what effect they each have on driveability, performance, and longevity.

There are folks who literally think they need a stage 3 clutch as a standalone performance improvement...

I've been to enough G35/350Z meets to know that the cars running a solid mass flywheel simply by listening to them idle. I don't know what clutch was in the 350z and neither did the owner, it was bought at a used car dealer. Perhaps like him you have adjusted to the geartrain rattle and simply drone it out much like a smoker who can't smell his smoking. An unsprung clutch with a SMF isn't absorbing any of the natural vibrations going through the crankshaft which means it's going through the driveline and gearbox. Car was engineered and designed around a DMF for a reason. Anything under 1500rpm such as creeping in traffic is not pleasant. The JWT kit was the standard because a DMF was crazy expensive and it was significantly cheaper. Now you can get an OEM dual mass setup for the same price. I also believe that's s strong selling point too in the future. If you want performance go JWT and SMF. If your car is a daily and commute includes morning and evening traffic daily I'd go DMF for driveability and comfort.

Also keep in mind there's quite a few different SMFW and I know for fact the ALUMINUM ones are loud as hell, in fact they almost have an "echo" to them. I'm using a lightweight STEEL billet one that does have chatter. Regardless tho switching to a single mass will introduce NVH because the 6MT is an INCREDIBLY noisy transmission when in gear and running at a low input shaft speed.