Hmm... might still be something up with the AMD drivers and the DX9 API mess that keeps rearing it's ugly head. Perhaps even the Xfire could be knackering things a bit (seem to recall they had issues with it back in the day). Sure.... the chips may have some age on them, but they should be pretty good for this game. MIGHT be able to offset the dips a bit if you still have some headroom to bump the memory clocks a smidge... seemed to be where I got the most benefit with my old Sapphire Vapor-X in my old Gigabyte based Intel system.
May want to squat dead center on a telepoint, go into first-person view, and look down into the middle of the telepoint to see what is getting hammered most in your system. Can use task manager's performance tab and/or something like GPU-z's sensors tab--both have the option to stay always on top, so you can still see them while the game is focused. My old i7-3630QM in my laptop rides single-digit %'s, while the nvidia GTX-670MX is spiking to 58% trying to keep the frames up. I stave off the frame dips on this old 2012 laptop by bumping the GPU's ram clock and core just a smidge.
To get the full impact of the load, need to have the point of the crystal's base in the center of the screen, otherwise it drops considerably. Attaching a screen grab of the view I am talking about at the telepoint.
You can do the same thing with the apps up while running around town and such as well, this is just the quick and dirty way I used to always tinker with my old PC rig when I played retail. It is about as consistent a setting as you can get other than sitting in your mog house watching your moogle spin and such.
Attachment:
File comment: Screen grab while /heal and looking down at center of telepoint crystal
Raistlin_2018.12.26_222550.png [ 298.65 KiB | Viewed 4180 times ]
Raistlin_2018.12.26_222550.png [ 298.65 KiB | Viewed 4180 times ]