You posted in the other thread that you have the Samyang 12mm I think that gives you two 'quality' options:-
1 Lee 100mm filters, as I believe that the Seven5 will be too tight on the 12mm
2 Hitech either 85mm or 100mm ranges
I went for the Hitech 85mm range for my grads, but all my plain ND filters are the screw in type, as you are less likely to get light leaks on long exposures. I'm slowly converting over my plain NDs to Hitech Firecrests, as these are quite neutral, but not cheap, so the process is a slow one!
Stupar's set quoted above will be too tight on the Samyang 12mm, thoigh they are fine on his 18-55, but even then might be tight if he starts stacking several filters.
Lee have great re-sale value, so if further down the road you'll get a lot of your money back on selling them. From my experience Hitech Firecrest Big Stoppers, 10,13,16 are more neutral than the Lee Big Stopper. Both companies only make this filter material in batches, so can be out of stock at certain times.
Hope this helps