I played the Sttafs on their own (ie no sub) for about 6 months. They have very good low end, especially for their size. The speakers I upgraded from provided deep bass - flat to 22 hz, and it wasn't until I played my old progressive rock cd's that I decided something was lacking. If your tastes don't include rock and progressive with deep bass tones as a key element, then I imagine you'll be quite happy without adding a sub.
If it were me, and I believed I wouldn't need a sub with the Sttafs, I would certainly give the Hawks a try (if trying them is an option). I think they buy you about 5 hz deeper extension (ie 38hz - 33hz), but the bigger advantage from what my salesman told me is tighter and more precise - whether it's enough difference to impress you can only be deternined one way. When I bought mine, I maxed my budget with the Sttafs so decided not to look further . . . The great part about them is I had no regrets that I didn't have more money - they're such a great sounding speaker - but I think this is true about the entire Totem line.