|yup, when it squats, you get more camber change, great for cornering, but not ideal for traction. If I was to go for IRS, I'd want long wishbones to minimise the camber change on bump, but if I made long A Arms for it, I think I'd run into flexing issues, especially with an LS1 (or a LS6) lump under the bonnet and some hefty rear tyres. There's a lot about IRS that's fantastic, but there's a few downsides (flex, squat, complexity, toe change when losing traction on cornering) which are quite fundamental.
A de-dion back end has a few different issues (rear wheels still tied together, potential beam flex, plus I don't know how strong I need to make it), but avoids the issues for IRS. I can also add a small amount of static toe in for stability, and have a play with static negative camber.
But hey, given my decision making history with this car, god only knows what I'll actually end up with!