Do your W&B and work out a civilised fuel load to use. It's amazing how much weight it can contribute to the equation overall. As long as you've got a good refuelling point reachable with (say) 20 mins flying you're laughing.
Practice lots (if you've not already done so) before you take a load on, to ensure you are confident at pegging speeds, landing spots, rotate spots, decision points EXACTLY where they should be.
Then work the load up progressively & compare against W&B/performance calcs, rather than throwing everyone in and hoping. You may well find that the way you fly the aircraft will mean a difference between theoretical & actual.
Don't forget to ensure you are hot on x-wind t/o's & landings too, if the strip is one runway. Sod's law you'll always have a 10kt x-wind when you want to fly.
On the Archer vs Warrior front, remember that many Archers have a coarser pitch prop (cruise prop) than Warriors. The Barton Warriors get off the ground pretty quick, even with a good load on, but they dont necessarily cruise v.fast. The Archer can take some time to wind up its speed, but cruises much better.
Summary? Go & rent a Warrior for a few hours and explore its capabilities thoroughly at a civilised grass site.