Tapering would be the best option if we were in the market for new sheets. Our spinnaker's 1000 square feet. 5/16" would tear off fingers a good puff, so our sheets are at least 5/8".
And you crew doesn't use gloves, winches or ratcheting blocks to help with the load? 5/8" is ridiculous for a boat that uses 1000sq ft chute. The load is less than 1,000 lbs in 15 kts apparent. In light air you won't be using a winch, and the heavy sheets hurt performance. When the wind picks up, you're using a winch anyway, what's one more wrap?
Check out the big boats, they don't have anything that's over 1/2". They just use higher tech lines.