Glad to have you back. The 166 GL/GLE/GLS are fantastic vehicles. I have one of each and yes, I like them that much. I chose a loaded GLS450 over a GLS550 since the M278 has been a bit very problematic for many and the 450 gets great hwy mileage. Hope you have no issues with yours. The 450's styling is a bit bland, so I purchased a GLS63 body kit for the 450 that I just haven't gotten around to installing.

Glad to be back. I kinda dropped off this forum because the GL/GLS forums don’t get much action.

The 550 is a true beast. It makes me wonder if a GLS 63 AMG is even necessary as the 550 is quick enough. The 450 is a great vehicle also if you’re more focused on comfort and highway driving instead of more performance that the 550 offers in addition.

The 63AMG bodykit should definitely give your 450 the much needed appearance upgrade.

The 63 is in an entirely different league from 550 with better seats, handling, acceleration, and braking. Now, you can get a 550 with a tune, active curve, and upgrade the brakes and make it almost a 63 but it still won't be there. Then again, you can add a tune to the 63 and it will be that much faster. However, given the propensity for these engines to implode with a tune, I don't recommend doing on either engine.

Love my 63 for what it is but it rides and shifts way rougher than the 450/550 and eats gas and rear tires like they are going out of style. It's almost too dedicated to being a sports car, which it is not, then an SUV. When the GL63 was released, it out-braked a Porsche Caymen S from 60-0. The brakes out of this world good.

Thank you for the little tidbit on the tune. I was actually curious about getting the Renntech tune 540hp 705 lb ft tq on my 550. Are all tuners unsafe for the 550? Renntech supposedly is the preferred tuner due to being the most safe or is this not the case? You know of actual experiences with blowing up the engines with the tunes or is this just speculation?

The 63 seems unnecessary and overkill for a 3 row SUV the 550 is fast enough almost too fast for a family hauler of 7 passengers. If I want to go faster, I’d want it in a sports car. I’ve seen some posts on Active Curve headaches even dealers have trouble diagnosing.

Renntech is a great tuner. I've used them before but the M278 in the 550 is inherently week and has a tendency to scuff the cylinders. Add more boost and the scuffing will happen even more quickly. Would just enjoy it for what it is. If you had a bi-turbo 12, I would say absolutely go with a Renntech tune. Those engines are bulletproof. On my old CL600, I picked up around 105 RWHP with the tune only. The additional power was amazing. Again, I don't recommend anyone's tune on the 550.

Similar to OP, I got a Lx570 as a family hauler then moved to a GL350. We came from a sedan and a coupe, so the LX570 "boat ride" road manner bothered us a lot. LX570 tilts at steering inputs, making us fear of roll over (same feeling in tacoma TRD), not that it would flip that easy. We know the LX platform is extremely reliable, my brother has a 19y old LX that hum along with regular maintenance.

X166 road manner is so much better. The platform is pretty solid for mild offroad. The whole family has been enjoying it. Maintenance and check engine lights are headages as x166 age. There are worries of things breaking when we take it on long road trip or offroad. However, the enjoyment factor outweighs the headage for us so far.

We don't drive fast with kids this X166. Living California, the numerous electric cars would out-accelerate pretty much anything even gas exotic sportcars.

That's a diesel thing and not necessarily one that encompasses the X166 platform. I have three that don't have those traits.