So here's my latest attempt at trolling - I finally put the GH round 3 keycaps on a Filco MX blue and used it this way for couple of days, but not full days due to busy schedule.
First impression - the keyboard now feels more like BS. I even put a BS keyboard and did comparisons - yes, they still differ in both feeling and sound, but the gap is much smaller now. Didn't expect that much of a difference from the keycaps, hence my surprise.
Second impression - my mind perceives shorter travel, which is of course ridiculous.
Third impression - Filco keycaps are nice. I knew that anyway, but I wanted to inform all the whiners. Whoever at Diatec wrote that they fine-tuned the keycaps is telling some truth. They really have distinctive feel and sound when combined with MX blues.
Fourth impression - SP keycaps are nice. Different than Filco's, but still nice. On MX blues remind me too much of BS.
Would be interesting to hear how SP on MX browns fare. I don't have second set to try.