Syndicate Base Stage Boosts:
Stage 1: +5% Building Output
Stage 2: +3% Double PvP Loot Chance
Stage 3: +10% Fight Respect Payout
Stage 4: +5% Building Output
Stage 5: +3% Double Epic Boss Loot Chance
Stage 6: +3% double raid boss loot chance
Stage 7: +3% lockbox open rate
Stage 8: ??
See Post #7 by Stubby for a detailed SS img.