Amazing! Thank you. Ordered

@jphughan I so far haven't been able to achieve 4k@60hz AND USB 3.0 speeds using my 2017 MBP, but is that more a function of the laptop than it is the cable or display?

@Vexir  It would help to be more specific about your MacBook Pro model, since the 13" and 15" models can differ in an important way here.  4K 60 Hz plus USB 3.x requires that your source system and display both support DisplayPort 1.3/HBR3 or better.  Most systems and displays on the market today only support DisplayPort 1.2/HBR2 over USB-C.  If that's all that's available, you can only get either 4K 30 Hz with USB 3.x or 4K 60 Hz with USB 2.0.  I wrote a long explainer post about the various operating modes of USB-C and TB3, including their impact on possible display setups, over here if you're curious.  And for that matter I wrote an explainer post about the differentiators of USB-C and TB3 cables here too.

But back to your display.  The U2720Q supports DisplayPort 1.3/HBR3.  As for your system, if it's a 2017 system and a 13" MBP, then it only has an Intel GPU and therefore will only support DP 1.2/HBR2 over USB-C since Intel GPUs back then didn't support anything newer -- in fact the Intel GPUs in SOME of the Core 10th Gen CPUs STILL don't support anything better.  If on the other hand you have a 15" MBP, then the discrete GPU will have control of the display outputs, and therefore the system MIGHT support DP 1.3/HBR3 or newer.  Newer 15" MBPs definitely do, but I'm not sure where that changeover was for the 15" MBP.

Lastly, note that even if you do have DP 1.3/HBR3 or better support on your system side, you might need to specifically set the display to allow 4K 60 Hz + USB 3.x.  It might default to running 4K 60 Hz and only USB 2.0 simply to allow 4K 60 Hz support from a broader range of devices, such as the majority out there that are still limited to DP 1.2/HBR2.  Otherwise, if the display always enabled USB 3.x, then DP 1.2/HBR2 systems would be limited to 4K 30 Hz, and Dell probably figured that most people would prefer 60 Hz than USB 3.x, especially given that they might not use the USB ports at all or might only plug things like keyboards and mice into them.  (If you read the explainer post I linked about the various operating modes of USB-C, you'll understand why this option exists.)  On Dell's newer U Series displays, the choice of how the display configures the USB-C link is managed through a setting called USB-C Prioritization.  You can read about that in the manual available on support.dell.com.

Thanks!! That's a really helpful breakdown. FWIW, my MBP is the "MacBookPro14,3", or 2017 15". I'm not sure where to find a more specific model number than that, though I'm aware of the weird MMHADLLA/A type numbers.

@jphughan Two problems: 1) I'm not able to get this cable to operate at 60Hz. That works on the old cable, and I didn't change any settings when switching over. Any advice. here? 2) I realized I actually need a longer cable. Not by much, maybe another foot, but you wouldn't happen to know of the same or similar specced cable that is longer? I looked at this seller's Amazon store and this is the only length they even sell.

@Vexir  For 60 Hz, did you set your USB-C Prioritization setting to High Resolution? If your 2017 MBP is only DP 1.2/HBR2, then that will be necessary when connecting over a regular USB-C cable so that all four lanes get allocated to video as occurs with USB-C to DP cables. But that will also limit you to USB 2.0 data speeds.

As for longer cables, 6 feet seems to be the limit for passive USB-C cables that support video, at least today. The only other option I know of is an active USB-C cable like this one, but that limits your power delivery to 60W, which is less than a 15” MBP is designed for, so you might see slower battery charging and/or reduced performance. The only 10-foot USB-C cables I’ve seen that handle 100W will ONLY do power and USB 2.0, and even then they’re pretty thick.

I don’t know of any 7-foot cables. Usually the lengths available are 3, 6, and 10 feet, or (fairly similar) 1, 2, and 3 meters.

@jphughan It is indeed set to high resolution. I just switched the cables back, and now my old cable won't deliver 60hz either! This was working this morning - now I'm just thoroughly confused How do I get my 60hz back? So sad.

Okay, I am sure this is some kind of bug but I was able to get it to 60hz on the original cable again by flipping resolutions in MacOS. I'm honestly tempted not to try the new cable again, lest it disrupts the 60hz again and I can't get it back. 

Dell if you're listening, this stinks! Please work with Apple to improve your MacOS support. I'm sure there's a good chance the issue is on their side, but either way, this needs work.

@jphughan Thanks for all your help. I'll probably end up returning the cable, but for anyone else that wants to give this a try, I'm glad this is searchable on the internet - it's a common question without a good answer, until now.