Hi Darren,
I used both Max GT and SMP recently at Bugatti, I also used YGK Ultra Castman. I like all 3, I agree totally with Brandon, the regular GT was my favourite.
As you point out, SMP is the newer generation and is soooooooo smooth through the guides (like all Varivas)however, not everything that's new is necessarily always an improvement in all areas.
In relation to your comment in relation to line diameter, PE is the 'designation' determined by diameter, therefore one PE8 should not be 'thicker' than another PE8, breaking strain does vary markedly depending on quality and technology. Hal Harvey wrote an excellent article on this in the Western Angler some time ago, a search may turn up that article.
AWP