1440p 120Hz display on a Mid 2015 15" MBP ?

[Antares23]

Hi,

So I've just ordered a used Mid 2015 15" MBP, with a i7 2.5GHz, R9 M370X and 16GB of RAM.

I currently have a Late 2013 iMac (i5 3.4GHz/GTX 775M/32GB RAM), and I'm thinking about replacing it by the MBP., I think the CPU performance is comparable, and as I don't really do anything that's really graphics intensive, I think the R9 M370X might be enough for me, even tho the 775M is more powerful. It might just be less of a hassle to use a single computer as both laptop and desktop, considering I might upgrade the MBP to a 1 or 2TB NVMe SSD down the road

So, what I'm wondering is, if I replace the iMac with the MBP, what's the max supported display resolution/refresh rate ? Either through HDMI or miniDP/Thunderbolt.
I'm thinking about either getting a 27" Thunderbolt Display, or I'd like to get a 1440p 120hz display, or a 4K 60hz.

From what I can tell from MacTracker, I can run 3840x2160@30hz, 4096x2160@24Hz trough HDMI, and up to 5120x2880@60Hz through Thunderbolt
But do you think 1440p@120Hz might work ?

I read a post here about people saying they managed to drive a 1440p 120hz with a 13" mid 2015 with a DP to Thunderbolt2/mini DP
And on there people saying they can drive 1440p 120Hz with a miniDP/Thunderbolt to DP cable

Can anyone else confirm (or deny) that you can actually run a 1440p 120hz on a 2015 MBP ?

Thanks !

 

[joevt]

A 5K60 display has a pixel clock of ≈960 MHz which requires two DisplayPort HBR2 x4 connections over Thunderbolt so you can only connect one of those. You could do 5K30 with a single HBR2 x4 connection but old Radeon chips have artifacts with width > 4K.

You can connect two 4K60 displays to Thunderbolt. 4K60 has a pixel clock of ≈533MHz.

1440p120 has a pixel clock of ≈498 MHz so you should be able to connect two of those.

HDMI 1.4 is limited to a pixel clock of 340MHz which is enough for 4K30 or 1440p60. If you could get it to do 4:2:0 then you can get double that if you don't mind chroma sub sampling.