Towing - Standard vs. Load-Leveling Suspension

[digdesign]

Hey Guys. I'm mew here. Been lurking on the forum as I've been shopping for a pre-owned E70 35d. Thanks for all of the useful info. Here's my question:

I'll be towing my E30 M3 on an open aluminum trailer. The total weight of the loaded trailer will be roughly 3800lbs (2590lb car + 900lb Trailer + 300lb spare tires & tools). Shooting for 10% tongue weight would put it at about 380lbs on the coupler. On top of that, I'll also have 170lbs of equipment in the back of the X5. So the total load on the rear axle will be in the ballpark of 550lbs.

My question is, does 550lbs necessitate the load-leveling suspension? I know that it will be "better" with it. But can anyone comment on the amount of sag I might experience with a standard suspension?

FWIW. I do want the load-leveling suspension, but it's hard enough to find a decent used 35d, let alone to find one with option 220 and no 3rd row. (I don't want the 3rd row since I'm towing long distances and need to carry a spare)

Any advice would be greatly appreciated.
Thanks
-Mick