Martial trances increase dodging, blocking, and accuracy by something like 5x (not sure of the exact number) but it basically allows the dwarf to become immune to all weapons and dance around blades like a drunken, steel-plated ballerina who's caving in skulls. It's glorious.
Whips have a relatively large size for their, well, size. The entire weapon is counted as the size, so the whip's handle, rope, and tip are all counted as part of the weapon. While a real whip strikes with just the tip, a DF whip strikes with the entire bulk of the weapon, but at the same speed. Imagine having a bull whip, but imagine that it's about 15x larger, made of solid silver, and moving at the speed of sound, concentrating all that force onto about 3 square inches. It's brutal, and the weapon data needs a little bit of cleaning. Most modders change the whip size to be very small and it works well enough.
Marksdwarves never train quickly. I put mine on a wall behind fortifications with my front door locked. They shoot, and they cannot run out to melee, so they stay safe. There's been a lot of science dedicated to handling marksmen.
10x Serrated Steel Blades means 10x damage, and 10x chance to get a body stuck and jam up uselessly. Most people make a 10x longer entrance and fill each with 1x disk, for maximum jam prevention. Although overall, dodge-em traps are currently in style and quite powerful. A forum search should yield numerous results for that design.