I'm stuck on 1.6 with mods like Thaumcraft, Tinker's construct, Hungeroverhaul, Extra utilities, Botania, Blood magic, Artifice... I have no mods at all which adds machinery (of course I do have Extra utilities generators' but I'll not use them at all, the enderquarry is pointless and will require too many generators, whereas a tunnel bore or the Ritual of magnetism can do the trick more easily).
Machinery is irrelevent. Any mod that adds any recipes will contribute to load lag and GT related load times, no matter how simple or complex. It's simply about quantity. So a mod that adds a ton of recipes, regardless of if they're simple or even vanilla-like, it still going to make Forge's sequential load method take ages, and as we've established, GT scans the Forge recipe database on load. Thus, you have the problem- too much stuff.
Also, you've named a LOT of the kind of mods responsible for this. That is a HELL of a lot of recipes you have added in there, several times more than MC has vanilla. More than GT adds, even, by a large margin. So what we're looking at is your modpack has more recipes than 'normal' by a factor of ten or more.