Hi Aaron,
During the Transatlantic S2S parties, many operators, including myself did several S2S DX QSOs using SSB.
My most recent S2S DX happened yesterday. I did a QSO on 15m with @AJ2I who was on W2/GC-076, but it was just above the noise level for both of us.
The antenna I used for all these S2S DX was my home brew 7-band EFHW, configured as inverted-L. The power was between 5W (no speech compressor) and 10W (with speech compressor). The bands I used were 20m, 17m and 15m. Soon 10m should work as well.
If the conditions are right, nearly every antenna will work, even with little power.
Once during Winter time I did a DX contact on 40m with a shortened EFHW, albeit it wasn’t a S2S.
73 Stephan