Sorry I meant to include this about the HD4000, you're totally correct. It and it's 3rd gen sibling actually support HDMI1.4, but fall into the
'Some displays and adaptors may be >1.3 but limit what they will output or display.' category, unfortunately.
Here's my rudimentary/half forgotten understanding gleamed from the PCH datasheet and random internet browsing:
* HDMI/DVI both use TMDS and share the same encoding/formatting for video and control. The Intel chipsets defines 9 TMDS lines for a port which are identical/interchangeable between the HDMI/DVI ports: 3 Data pairs, 1 control pair and the hot plug detection.
* The 3 data pairs, the control/clock pair and the hotplug pin form the connections of a single link DVI-D connector.
* The DVI spec identifies the max pixel clock of a single link DVI connection as 165Mhz
* Higher pixel clock requires dual link, via an extra 3 data pairs, which are not defined by intel in the datasheet
* HDMI uses a single link connection, with 3 data pairs, control pair, and hotplug. (Except type B connections which were dual link, but never actually produced by anyone)
* HDMI * HDMI1.3 upped it to 340Mhz over a single link. Which is incompatible with DVI, which increased max res by adding more lines, rather than change the existing ones
This is where I make a bit of a leap: as far as I know, since the lanes used for HDMI/DVI are defined interchangeably, they are limited to a max clock of 165Mhz, the DVI maximum.
So even though these cards are listed as HDMI1.4, the video data produced is effectively maxed at DVI-D single link/HDMITL;DR again: the intel HD graphics (Specifically the HD4000 and HD2500, but assumably the earlier ones as well) are limited to single link DVI-D and the equivalent pixel clock over HDMI, effectively 1920x1200. DisplayPort does doesn't share this. If you have an Intel adaptor, and want >1920x1200, you're gunna want to use DisplayPort.