I believe that these days Dexed is the preferred environment for people who make presets that they're subsequently going to play on an actual DX7, it's that good.
For what it's worth, being "that good" is relatively easy for a DX7 compared to other synthesizers since it's a purely digital design and the algorithms (in the software, not FM sense) are pretty straightforward. It's not like emulating, say, an Ensoniq SQ-80, where you have to emulate analog filters which always involves a level of compromise and approximation.
