Hi DocBullseye. Welcome to Geekhack.
You stumbled upon some great switches for a first mechanical board. I like Outemu blues more than MX, and I think they're almost indistinguishable from Gaterons. I'm no longer a fan of MX and MX clones at all, but if I had to use them, Outemu or Gateron blues would be one of my go-tos. That K660 is an interesting-looking board. Maybe a little flashy for me. lol
The Drop CTRL does look like a great board. I have the ALT and it seems very solid, although I haven't used it much. I mostly got it because I found one for a good price and didn't have any hotswap boards for playing with switches.
What switches have you got in that GMMK? People seem to love those boards, for what they are. Those caps are pretty sharp looking.
What switches did you order? A big switch tester is usually a good idea, with as many different types as possible.
If you want a heavier, clicky that is MX compatible, I must always shill for the Kailh box jade and navy switches. I think they're the best clickies available with MX compatibility. Linears feel like nothing, really. You can't compare them to rubber domes because those are tactiles, and being rubber they bottom out relatively lightly. With linears, unless they're dampened, you've got (relatively) smooth travel from top to bottom, depending on the switch and if you want to get into lubrication (I don't).
I would avoid that K620T. It looks great, but Ajazz switches are literally
the worst MX blue clones I have ever felt in my life, and MX blues are already unusable for me these days.