For assumed typical DD function/features (ie: visit modern websites), Vanilla Darkweb is my recommendation as the best compromise between function and speed out of the box that we currently have. Certainly you can tweak either IWPPC or DW to improve speed and function as Erik has done extensively with TFFx. I use IWPPC & DW on G4 and up machines, reserving DW for my more modest, single cpu, sub 1 ghz g4 boxes. I typically pivot to Links2 or Retrozilla browsers on my g3 machines and between those two, my preference has been Retrozilla as the web experience L2 provides while insanely fast, is graphically challenging for me to use comfortably. Certainly others here have no issue and use it comfortably.
I also liked Webkit for its speed but it has always been prone to crashing for me and the sites I visited, so was a pita to use. Stability & comfort/familiarity ended up being more important (and still is) than speed. Anyhow, lots of good info in this thread. Best of luck to you.