To be honest, if you're going to spend that much and want it to last practically a decade, and plan to use it for design, programming and heavy multitasking, I'd consider going all in, just for the RAM boost alone. While 36GB is plenty for now, 48GB would really give you some future-proofing and long-term breathing room. The 33% faster GPU couldn't hurt either. Just my two cents.
Edit: Something else to consider, it's possible this MacBook line may no longer be supported by new OS releases after 8 years. You could always get the lesser model now, and sell it after 4, 5, or 6 years and upgrade again. It might be wiser to not overspend on a current model, save a bit of money and just upgrade a little more often than every 8 years. For example, you can probably still get $2000+ for this after a few years, and upgrade to an M6-M7 machine at that point.