It sounds like you use a 4k with it normally, anyway though? So for day-to-day it is still good enough?
Not good enough for me, no. I'm waiting to see what the next MacBook Pro brings to the table.
The entire design of the 12" MacBooks is based on providing short bursts of relatively good CPU power - the turbo-boost speeds for these little processors are quite respectable.
However, this means if you put the CPU under continual stress, the MacBook - and the surface it's on - will heat up, severely impacting its ability to dissipate heat. The CPU is then forced to throttle and you won't get the turbo speeds you're used to. That's when performance gets impacted. It's really simple physics.
From my experience, driving 4K worth of pixels is just too much continual load for these little machines.
I'm in Copenhagen on a trip right this second and brought my little MacBook with me. It fits in the safe in the room, was great for Netflix last night, and was so light to carry around today in a bag for ad hoc research and looking at our photos from the day over coffee. It's bloomin' brilliant. But it's not the right product for you. The Pro is.
Again, I stress to everyone - if you plan on regularly using your 12" MacBook with an external display, you are buying the wrong product. Apple has never, ever developed or marketed this product for that usage. It is an ultraportable that runs macOS and relies on the user utilising wireless technologies to get the most out of it. And it does that great - almost perfectly in my experience.
He's an optimist, like me, and loves his MacBook 12 well enough to have bought that 4K display to be ready for the spring 2018 refresh.
I bought a 4K display for my gaming rig. I made sure I bought a USB-C capable display for use with Macs.