Sorry Rolex fans, but I feel explorer 1 @ 10k is abit dated. It's a classic and will hold value, but for wedding purposes probably not such a good buy since its small and understated. For a more modern choice, 2nd hand Planet ocean or a brand new 2500 Seamaster 300m is quite nice. Unfortunately no rolex sports watch other than explorer 1 @ 10k range.
2nd hand Panerai also available for base models if you are willing to stretch ur budget to 11-12k. If around 5-6k probably a nice auto Ball/Longines/Tissot is good too.
If the groom knows anything about watches, a Rolex is sure to be appreciated. Really.
If all you want is something blingy, large and just to show-off in front of a crowd of easily impressed wedding guests, just get one of those super-large shiny Invicta or Ingersoll watches. They cost well below 10K; they look impressive in a showy kind of way.
It all depends on your intentions for the gift. If the gift is merely to fulfill a social obligation of bringing something nice to the reception, save money and buy a cheapo flashy watch.
PS:
You can get a nice brand new quartz Tag Heuer (Link or Aquaracer) or Omega (seamaster) sports watches at the original 5-6K range. At 10K, you can get a brand new Tag Heuer 5000M Aquaracer (the one Leo DiCaprio shills). I forget how much a brand new basic model Omega Bond Seamaster (300m) costs, but it should be around 10K.