The M50 is rated at 520hp at the crank, the SQ8 500. The SQ7 dynos show it's making about 550hp crank in the real world, something like 470 wheel as I recall. The M50 dynos at about 520 wheel, meaning it makes like 600 crank. Couple that with not being forced into a air suspension, etc... the BMW is definitely the sports car of the bunch. The SQ8 looks like a wannabe Urus, sure. It probably is lighter than the SQ7, so it might flip the script on the X5 vs the SQ7. But the X5 drives great. Throttle house just did a X7/GLS/RR comparo, all with V8s (the X7 was an M60i and the RR uses the V8 from my M50), and the GLS580 got wrecked in it. I think the MB is by far the weakest offering between the 3 mainstream Germans.
The new M60 has a detuned S68 M motor and a 48V mild hybrid. It is admittedly quicker than the M50, but is claimed to make the same power. The hybrid motor just helps it off the line that extra bit.
If it wasn't for the kids (plural), I'd have had a long hard look at the X3 M40i (well, I wanted the X3MC, but same people would got M40i). It's objectively better... better on gas, the B58 is more reliable, the vehicle is more fun, basically as quick... But it didn't fit car seats behind me, which would have been fine with 1 kid, the car seat could go in the middle or behind the passenger seat where my substantially shorter wife sits. But with two kids, no go. Macan would also be a sporty choice here too, or SQ5. They're OK, but always feel small to me. They're like big hatchbacks.
Congrats on the baby! You say one and done now, but in a few months you're gonna realize your baby needs another baby to keep it company. Or you get to where we are with a 2 year old and you miss having a baby around, so you have another one, lol. We knew we wanted 2 , so we just did that, and are continually reminding ourselves that we do not need 3, no matter how cute these 2 have been.