I was very impressed with the Lateral Dynamics 3 link on Bad Penny, this system would have to be rated at the top right now.
It's not like you really notice "wow, this rear suspension is really working". It's more like you don't notice any instability or bumps upsetting the rear, often getting something right just takes it away from the driver's perception of it. I also found that the case with the Bilstein shocks on Penny, there just wasn't an issue raised with the shocks. My hat's off to Steve's Bilstein guy.
The car did everything I asked of it and was very easy to drive, yes we had understeer, but other than that, the whole package just flat worked very well. A large part of my getting good results in the car was how easy it was to just hop in and drive the snot out of it!
The rear did NOTHING funny, put the power down VERY well from standing start to 95mph curves at 1.2g's
I'm a big fan of leaf springs, I think the only drawback they have is higher unsprung weight, this makes them less ideal for ride characteristics. You can put spherical bearings in them like GW cat 5, but those springs are very stiff and you feel the bumps much more through the bearings. Stock rubber front bushings are better riding but I'm sure you lose a little bit of directional stability.
Hopefully I will be working hard on my 67 Camaro this winter, and am now trying to choose what rear suspension I will use. I am torn between just throwing the Hotchkis leafs on it that I already have and suspect will be a tad soft, or going whole hog on the LD 3 link. With a roll bar in the car, I doubt I'll ever put a passenger in the back seat, it would be suicide. It's just that this was my first car, and I will be keeping it fairly stock looking inside, without the usual PT bling, I actually LIKE the factory gauges, -but it will be kinda serious in the engine and suspension dept.
I see a lot of value in the DSE quadralink, G bar/Air bar, Speed Tech torque arm or Alston rear. I doubt anyone driving on the street would need more, not to say they would not work on a track at all, there is no reason they should not work great. It's hard for me to comment on them since I haven't driven cars with them.
Lap time wise, I doubt there is a big difference between any of them, but for the highest driver confidence / comfort level, and tuneability, I'd lean towards the Lateral Dynamics 3 link. The things I don't like about it are the extra tubing/bracing/linkage for the bellcrank. I'd like to use a 12 bolt rear axle, but access to the rear cover would be tough. I think I'd have to switch to a Ford 9" rear.
David