Sled lots, Ahem I mean independent car lots can be dicey.
A clean Carfax showing no accidents doesn't mean its never been wrecked. This XT6 prospect could be a Cadillac trade-in that was inspected and wholesaled because it has issues such as too much paintwork, panel(s) replaced, even a leaking cylinder head. I was in the used car inspection business for over 20 years. Anything is possible with a used car.
I would lease a new XT6 and you might be able to have a much smaller payment than $900 without putting a huge amount down. The '24s are coming, they want to move the '23s. Its a big country, cast a wide net and search. New is new no matter where you buy it. Memorial Day, 4th of July, Labor Day are ALL big car promo times, all coming up.
Cadillac is discounting too. I leased a '23 XT4 in March. MSRP $39,840, Selling price: $33,380. Price included a $2k current GM lease conquest rebate, but my current lease is on a Ford. They got it approved. $3079 down, lease payment: $379 plus tax so in CA "all in" payment is $415/mo. It basically was their standard national lease offer for the month but my XT4 was $2400 more expensive than the lease offer vehicle. Was there more discount to give? Only they know but I think it was a fair buy.
Cadillac has national lease specials and discounts every month. With mine, the the lease "money factor is" .00070. That's 1.68% interest rate. I usually buy 2 or 3 years old but with a big discount off MSRP, a new one can cost the same or not much more than a used one. Low interest and it makes more sense and easier to swallow the stretched out payments if I decide to buy in three years.
I would find two or more similar XT6s you like at different Cadillac dealers. Play the dealers against each other until you get the deal you want. The bummer about Cadillac leases is Cadillac won't budge off the 50% residual value. That's one reason lease payments are so high for some (plus the initial high price). If you walk away from your lease, you are "buying" or paying off too much of the car.
If you go with the '20 you can purchase a GM extended warranty from some GM dealers online for about 40% off. I would do that.
Almost forgot, check out some of the lease swapping companies. You may be able to "take over" an XT6 lease maybe in its last year or so. Then,when the term runs out, buy it or walk away. One is leaseswap.com and there are others.
Just my 2 cents. Your mileage may vary. Good Luck.