560-4 owner here. AWD is awesome if you want to go full HAM, cut up with the hoodrat boys on the streets, or plan on adding boost, but RWD is the way to go if you’re more into sliding around. The AWD system does feel clunky at low to mid speeds, but once you’re moving faster it’s a grip monster with tons of top end stability. On the other hand, 560 4s converted to RWD feel quicker and smoother since you’re not sending power to the front and everything goes straight to the rear wheels. The catch is, while RWD feels nice and easy at low and mid speeds, once you’re above 140 mph the front starts to get light and it can feel sketchy.
Aside from power, the big difference between the 550 and 560 converted RWD comes down to suspension geometry. The 560 was tuned for AWD traction, not RWD. So if you switch to RWD, you’ll notice it shifts from understeer to more oversteer, since the front wheels aren’t pulling you through corners anymore and it relies only on the rears. Something to keep in mind if you’re not super experienced. Clutch management is also a big deal when comparing AWD to RWD. We all know the number one question people ask when buying a Gallardo, "what is the clutch life?" lol. RWD clutch life is significantly better by almost 30%.
My take on this? Skip the 550-2 and grab a 560-4. That way, if you want RWD, just drop the driveshaft in 30 minutes and you’re good. I’d leave the front diff in though, to help keep the nose planted since the 560 was never designed as a RWD car. This setup keeps the 560 badge and hp rating, and you can still advertise it as a 560-4. Best of both worlds, greater clutch life for being a 560-4 car, not to mention the 560-4 is more sought after with better value retention over the 550-2.