Without knowing what your specific requirements and expectations are its impossible to provide targeted information to help you make an objective decision. Everyone else is selling something that may not even be applicable to you.
As for the soldered RAM, I've heard good arguments for and good arguments against it, dealing with security, or usability which are often trade-offs. An older model allows you to flash the BIOS with an open source alternative and to remove any backdoor functionality that may remain in Intel ME, AMT, or any of its related subsystems.
You also do not mention how old the T480 is, we can surmise based off its original manufacturer date that its older but components have limited life and part of the cost of buying something new is the guarantee it will continue working, and that its usable life has not been expended.
I've seen T480s that are running just as fast today as they were when they were brand new. The owners of these took extra steps to make that happen. Controlling heat play's a crucial factor, removing design defects are another. The pristine ones I've seen have fixed the fan failure by rewiring the fan power cables so they don't get routed over a heatsink (i.e. where IBM itself used kapton tape right on top of the heatsink), or replaced the low-grade CPU thermal paste with a more heat conducive binder.