I too owned the GST perpetual titanium just like yours and it was the worst timekeeper of them all. It was serviced three times and IWC could never get it right. That's aside from the perpetual calendar issues I had...🙄
I've had about five IWC's with that ébauche and all have been approximately +10 seconds per day. But, it is interesting to note that I had this antique recently serviced by my local watchmaker and it keeps much better time than all the other more modern ones.
And, at some point I had more than 20 of them. All modified ETA, modified Valjoux or in-house (8-day or otherwise) ran +8 to +15 seconds per day and none of them could be regulated by IWC in the US or in Switzerland. This, however, did not bother me that much because many of my other brands behaved
I had the pleasure of trying it on a few months ago and felt it was a great fit for my 7.5" wrist. Can't speak for this particular movement but I happen to own a number of modern PAM's with in-house movements that have proven to be rock solid and super accurate.