You won't loose any capacity Scott, they are pretty close, with the Dacron being slightly thinner as it packs down when you wind it on with plenty of drag. It will save you money in the long run, as the dac will last years, and you will only be replacing the 100m or so topshot regularly. 10 topshots out of a 1000m spool of mono. Just change it every season, or after a few fish when it starts to look a bit off.
Cheers,
Myles