the diffrence in oils is slight if your a basher. the thicker the oil, the harder it is to spinn the diff. you know when you hit a corner and the front inside tire free spins and balloons out? an thicker oil will resist that..not stop it!!, the goods and the bads? it is harder to control your rig on lose terain if your diff oil is very thick becouse, its easer to get all 4 wheels to spin out of control.. if you are on a high traction surface like grass, then a thick oil would be great. with a thinner oil on low traction surface, you will have more control for a faster hole shot becous the left or right side tires will spinn a little bit more but will keep you in a staighter line so you can stay on the gas.. you might think that a thicker oil might be a little more fun if your a basher but i think its more fun to have a little more control over my rig so i can get it up to speeds faster. i think i had 50k or heavier, but switched it out to 20k..