Outriders are special choice and a damn fine one at that. A noble ideal for human soldiers to aspire to, their expertise with technology makes them quite a valuable force. Here are some options to power them up.
Special Choice: Keep as is, but make them leadership 8 to represent their increased experience in combat. The Outrider Champion is still Leadership 8. The squad may take Heavy Armor at +2 pts a model, and Barding at +2 pts a model. If either upgrade is taken, the unit ceases to be fast cavalry. For an additional 5 points, the outrider champion may take a brace of repeating pistols.
Rare Choice: For +9 points a model, the entire squad may be upgraded to Veteran Outriders. At BS 5, they still carry repeating handguns, but for free, any of them may swap them out for grenade-launching blunderbusses. For an additional 5 points per model, the squad may all take a brace of repeating pistols. (35 pts a model for uber-pistoliers in essence). The squad in addition to all normal upgrades may carry banner for +7 points, which may be upgraded to a Magic Banner of up to 50 points.
Grenade Launching Blunderbuss: New rules. This weapon is a guess-range item of up to 18 inches in length. Roll a scatter die and a d6. On a roll of 1, the outrider takes a wound and must take a saving throw at -1. Shots from the blunderbuss are resolved at S3 armor-piercing, with the small blast radius. When a unit has multiple blunderbusses in a unit, guess with the first blunderbuss and roll for scatter. Then for each subsequent blast, roll a scatter die, and move another small blast marker adjacent to the appropriate area near that blast marker (in essence, this is the 40k barrage rule).