By how much does Fast Track boost your XP? I’m at Pioneer-8 and I was just wondering about it.
Usually 400-500 xp, It helps A LOT.
It depends on how much of the game you use it for. If you use it the whole game, you get around 20% more. (About 500 in MM and 1500 in Spartan Ops.)
I think Fast Track gives you approximately 1,000 XP in Spartan Ops.
It’s all about Mobility and Dexterity for me 
The longer you use Fast Trach the more XP you get. In the time it takes a standard War games match you would recieve about 20% of your total XP. (Granted you were using Fast Track the entire match.) A analysis and test about the total it gives you can be found here-> Analysis of Fast Track Tactical Package (Pioneer) - Halo 4
I’ve been using it and getting OVER 9000 XP in spartan ops.