Albert,
Could you expand further on your personal impressions of each stand's relative strengths and weaknesses in the context of your system, and why, ultimately, you opted for the Stillpoints vs. the GPA?
The Grand Prix has very bold bass but it's a bit flabby, it presents music in a soft and sweet manner reminiscent of Audioquest Sorbothane footers. All notes are a bit fatter especially the mid bass. Sound seems slowed down a tiny bit.
The Stillpoints bass is so tight, at first it seems something is missing. You may have to retune the system by moving speakers, swapping tubes or whatever tweak to put tonal balance back where bass is in balance again.
Ultimately the Stillpoints are cleaner, faster, higher resolution with better sense of each instrument placement and much better frequency extremes. They are also less money, take up less space and I prefer their appearance.
Remember I was experimenting to find the best resolution for my system to balance the new twin JL Audio Fathom F-212 subs. Tight bass for the main speaker was a huge improvement and allowed better integration with the subs.
Hope that helps.