Yeah, that's definitely too much thermal paste.
I think i saw a review or something one time where it was determined that Arctic Silver really wasn't that conductive, even when put on the board itself. Looks like it didn't mess you up anyway, as your card is running well now.
No matter how bad this was, it wasn't as bad as when I tried to do "preventative maintenance" on my fat 40 GB PS3. I had done thermal paste reapplications numerous times on laptops and desktops, graphics cards, etc., and though this would be a good idea.
Turns out that the large heat sinks they had on the PS3s would actually warp when removed from the motherboard. So I could never, ever, ever get it to meet with the two processors on the board again. I took it apart and reapplied the paste dozens of times, bought new thermal pads, and eventually broke it, getting the Yellow Light of Death. And of course I hadn't backed up any of my saved games.