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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
I found GCDRing to lag horribly and often reset or get stuck when spamming abilities. It has been updated since I last used it, so maybe those issues have been fixed.
/realises this post isn't a lot of help after all...
Hi, IF you do use AzCastBar which i think is a pretty good castbar mod, u could download the plugin pack which can be found here
and just pick the GCD plugin, scale and fix with it however you want.