Does Mac Pro (Late 2013) support 60Hz refresh rate at 4K monitor?

The LG 4K UHD 27UD88-W has one DisplayPort connector and two HDMI 2.0 connectors. As far as the LG screen itself is concerned all three of these ports should be able to do 4K at 60Hz.

The problem is that the Mac Pro only supports HDMI 1.4 and does not support HDMI 2.0. As such it can only do 4K at a maximum of 30Hz.

There is one other option you can consider, it is now possible to get a Mini DisplayPort to HDMI 2.0 adapter. This since it converts to HDMI 2.0 will allow 4K at 60Hz for HDMI. The best adapter I have found for this is this one - http://www.club-3d.com/index.php/products/reader.en/product/mini-displayport-12- to-hdmi-20-uhd-active-adapter.html

It must like this one be an active adapter.

So -

option 1 - get a Mini DisplayPort to DisplayPort cable

option 2 - get the above Mini DisplayPort to HDMI 2.0 adapter and use a standard HDMI cable

It works at 60Hz - with display port (Thunderbolt) - I am running it now on a 28"

but NOT on HDMI as that spec/port does not support 60Hz.

Get a mini Display port to Display port adapter for your monitor, IF it has a Display port connector

I think it doesn't support it, only 30Hz and 24Hz.

Using 4K displays, 5K displays, and Ultra HD TVs with your Mac - Apple Support