Much as I would love to just leave this game in my past... After all, as many of you likely know, it's a real bitch to sometimes get running well. Unfortunately, a distinct lack of games with the same level of storytelling make that impossible!

I recall downloading a patch on my last playthrough which fixed spell lag. It wasn't any of the major mods, I literally only had this one patch installed and it worked like a dream.

The only problem is, I can't remember who made it or what the fix was actually called... I just remember that it was focused around resolving the massive spell lag/FPS drop brought about by using spells.

Does anyone know what this fix is or have a link to it? Any help would be much appreciated!

Unfortunately I don't know which specific patch fixes this issue, in the link below you find the most common patches and mods for the game. If the lag was DirectX related, Aqrit's DDrawFix might do the trick.
http://www.moddb.com/games/planescape-torment/downloads

Aye, I've got the list of mods to install and will give it a try on that. I just remember when I got about half way through previously, it became unplayable until I found that patch.

Will have to see how it works then. If I can find it, I will be sure to post it on here.