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Can You Replace Your iMac 5K with a MacBook Pro and LG 5K Display?

Posted January 19th, 2017, by rob-ART morgan, mad scientist
February 5, 2017, ADDENDUM regarding flickering and freezing

As I was playing with the new LG UltraFine 5K Display connected to the 'late 2016' MacBook Pro, the question popped into my head, "Could this combo replace the 'late 2015' iMac 5K?"

Three of the four graphs below dramatize how well both Macs perform OpenGL animation at the full 5120x2880 resolution. LuxMark is added to compare the OpenCL render power of the two Macs.

GRAPH LEGEND
iMac5K - 'Late 2015' iMac 5K with 4.0GHz Quad-Core i7 CPU, AMD Radeon M395X GPU, 1TB flash storage, and built-in Retina 5K Display
rMBP + LG5K - 'Late 2016' MacBook Pro 15-inch with 2.9GHz Quad-Core i7 CPU, AMD Radeon Pro 460 (4G) GPU, 1TB flash storage, and connected to the LG UltraFine 5K Display

FurMark OpenGL - This "Burner Benchmark" stresses the GPU using an animated hairy donut flying through a worm hole. We ran it at 5120x2880 with no anti-aliasing.
(HIGHER frames per second = FASTER)

GFXBench Metal - Using the Manhattan 3.1 animation, we ran at 5120x2880 fullscreen.
(HIGHER frames per second = FASTER)

Tomb Raider - We ran the Built-in Benchmark at 5120x2880 using High Preset
(HIGHER FRAMES PER SECOND = FASTER)

LuxMark 3 OpenCL - The Hotel Lobby scene designed by Peter Sandbacka contains 4.97 Million triangles.
(HIGHER KSamples per Second = FASTER)

WHAT DID WE LEARN?
In terms of GPU (and CPU) performance, the fastest 'late 2016' MacBook Pro with the LG UltraFine 5K Display is NOT a replacement for the fastest 'late 2015' iMac 5K. The laptop's main advantage is portability and Thunderbolt 3. That second advantage should disappear with the release of the 2017 iMac 5K.

As for value, the 'late 2015' iMac 5K configured with the best CPU and GPU, 16G of RAM, and 1TB flash drive is priced at $3599. The MacBook Pro with the best CPU and GPU, 16G of RAM, and 1TB flash drive is priced at $3499. Adding the LG 5K screen at the discounted $974 brings the total to $4473 -- or $874 more than the iMac 5K. If you choose the more expensive, slower performing MacBook Pro combo, you can take comfort in having TWO screens, FOUR Thunderbolt 3 ports, a Touch Bar, and portability.

The LG UltraFine 5K display makes a great 'home base' companion to our 'late 2016' MacBook Pro. No plans to buy a 'late 2016' MacBook Pro? It makes a nice primary or secondary display for other Macs.

NOW SOME CAVEATS
Before you ooh and aah about the P3 wide color gamut of the LG UltraFine 5K Display, be aware that the iMac 5K Retina display also has P3 wide color gamut (ooh, aah). Also, both screens have a 500cd/m2 brightness rating.

As with the iMac 5K, the LG's default resolution setting is a scaled 2560x1440. If you attempt to set the LG 5K to a higher resolution than 3360x1890 while connected to the 'late 2016' MacBook Pro, it will warn that performance may suffer. That's puzzling since no such warning is forthcoming when you switch to 5120x2880 on the iMac 5K.

The LG 5K has three USB 3.1 ports on the back but they are Gen 1 -- as in 5Gbps. That's half the speed of the 'late 2016' MacBook Pro's built-in USB 3.1 Gen 2 ports (10Gbps). They could be useful for slower devices, though you will need an adapter if that device's cable does not have a USB-C connector.

Though the LG 5K display can be used as the primary display for other Macs, "Apple recommends that you use the LG UltraFine 5K Display as a second monitor with Mac mini and Mac Pro, as the display might not turn on until you boot into macOS. As a result, pre-boot features such as Boot Picker and macOS Recovery might not be available on the display." (We're used to flying blind with the Dell 5K display. We just memorize the order of the boot volumes.)

When connected to any Mac other than the 'late 2016' MacBook Pro, the LG's resolution limited to 3940x2160 at 60Hz. When we used the Option key to view more Display scaled options, it showed 5120x2880 --- and even higher resolutions all the way to 7680x4320! I assume that "60Hz" is the key metric. It likely drops to 30Hz or lower vertical scan rate at extreme resolutions.

If you are thinking of buying the LG UltraFine 5K Display, better make your move before March 31st, 2017. That's when the price reportedly goes back up to $1299.

ADDENDUM
MacRumors is reporting that some users are experiencing flickering and freezing issues with the LG UltraFine 5K display. Supposedly it is occurs when the display is in close proximity of a WiFi router. However, on occasion, we have experienced some flickering and freezing even though our WiFi router is at least 20 feet away.

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WHERE TO BUY A THUNDERBOLT GPU EXPANDER FOR THE MAC
Bizon Tech sells the BizonBOX 2S (works with all Macs with Thunderbolt 2) and recently announced the BizonBOX 3 (designed to use faster bandwidth of Macs with Thunderbolt 3).

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copyright 2017 Rob Art Morgan
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