Hi Alan,
There are a few local people on this forum who swear by the line - Allan L springs to mind, so they must be doing something right. I used to religiously use the Mallard for dry fly on both running & still water but since I've married the Olive SLX on the 4wt Helicoil I can't see past it.
I do have a 4wt GT90 and it's more than fine but I prefer the adaptability of the SLX at the moment.
Is it the best profile for what you do? I don't know. Is it a good line? Aye
Check out the reviews on the Barrio lines page of this website, might help.
Not seeing any reports from you?!
Iain