I believe the longer they are the more they will hold your axle stable
Any length will hold the axle stable. Shorter bars are used more for drag racing, such as Cal Tracs. You'll typically see sled pullers with much longer bars. Most seem to agree that around a 60" bar is good all around.
Some pictures of mine here: PMT Fabrication. TRACTION BARS FOR DURAMAX, POWERSTROKE, DURAMAX
07 CCSB 4X4 LBZ: Danville Billet 4094 & 45% Nozzles, DSP5 by Mark at Danville, BT Lockup Box, Romeo Fab Up-Pipes, Downpipe, & 3" Y-Bridge, Banks Hotside/PPE Boot, BD Manifold, Rail Shimmed, PCV Reroute, MBRP 4", S&B Intake, Airdog 2 165, Autometer Factory Match Boost/Pyro, Suncoast GMax 6-3/Precision ML built by Riley Gullett, MA Pump Rub & TC Brace & Big Hog Customs Trans Cooler Lines.
Cognito UCA's, Rancho 9000XL's, Rare Parts HD Tie Rods, All Season Centerlink Bracket, HD Idler Support/Gusset, Russell Stainless Brake Lines, Brake Performance Dimpled/Slotted Rotors, Custom Traction Bars, Line X Xtra, 6K HID Lows and Fogs, Smoked Headlights & Taillights.
BMF 20x9 Death Metal Rehabs with 305-50 Nitto 420S