For pure XP, mission objectives matter more than kills. is the fastest map. Pick the "Payout Objective" that gives the most XP (e.g., "Silent Assassin - No Firearms") and rush the penthouse guards. You can finish a Dubai mission in 90 seconds for 1,000+ XP.

Upon reaching Mastery Level 60 and filling your weapon wall, you can use the prestige laptop to reset your inventory for a permanent XP bonus multiplier.