did gddr5x end up reaching 14ghz? if so are there any differences or just in effect a rename?
Only in lab/walled conditions.
Highest offered was 12Gb/s, and there are subtle differences between the standards from channels to structure-number of pins for data/control/etc.
In their Micron technical notes manuals they mention 13Gb/s achievable for GDDR5X although not offered to public.
The biggest fundamental difference is what they call access granularity (read/write in a single flow cycle) and here GDDR6 is same as GDDR5 while GDDR5x is double and also channel count difference of 2 for GDDR6 vs 1 for GDDR5x that is part of the reason.
If you look at the data-control flow you will notice GDDR5x is not the same with command/address relation with data - not the data clocking frame diagram.
The double data sounds good on paper for GDDR5x with regards to access granularity, but one needs to consider this also increases the flow control mechanisms or longer delay for CA in terms of communication so has trade-offs and especially so if certain functions/applications require optimised memory in way of GDDR5 characteristics; we can see some real world examples that are impacted by GDDR5x.
Maybe it also impacts/complicates the development of higher transmission rates and why only 12Gb/s are offered for GDDR5x; context also includes the 2 channels with GDDR6 that are part of this in the way I mention.
I am surprised they are able to offer 16gbps and higher now for GDDR6 from Samsung, would had expected it to be around 12 months for mass production at those speeds.
Price must be a premium.
But even Micron are able to offer higher GDDR6 to their clients than their GDDR5x.