If you can find them the SX wings are the way to go. They extend further aft, which improves downwind sailing. The extension also makes solo sailing easier, as you can sit further aft, allowing you to easily use your feet to steer the boat while your hands handle the sheets.
For 2up (2 man crew) sailing I would guess the wingless boat would be faster in most conditions. For solo sailing it is hard to beat flying a hull while trapped out off the wing.
When flying a hull unnecessarily high the leeward wing will drag, slowing you down even more. Under ideal heeling conditions the wings stay clear of most waves. Steeper waves, like surf and wakes from large power boats will hit the wings. Although it can be a bit of a drag, it is not a huge deal.
As far as capsizing while on the wing, it can be quite scary. Without the wings you can fall 5' onto the boom, or 9' into the lake. With the wings the boom is 7' down and the water is 11' down with the other wing just below the surface. If I am out on the wing I always try climb over and bail towards the dagger board side. That said, wings are worth it. Wings make the boat more comfortable, spacious and add a level of excitement when trapped out.