Keep in mind that LE 10.0.2 will now output 10bit video files as 10 or 12 bit instead of only 8bit before - which obviously requires higher HDMI output clocks.
The hdmi pixel clock is actually the same.
12-bit YCC422 is 24-bits per pixel. Which is the same as 8-bit RGB444.
But the core clock does drive many parts of the SoC.
And it may be that a part of the chip that was dormant when we were outputting 8-bit RGB444 is now required with 12-bit YCC422 and has an overclock limit below 700MHz.