Personally I find commuting with front panniers on a front rack more stable than commuting with rear panniers. That includes climbing a few minor hills and decents at about 55kph. And there's a rear rack on the bike so its a deliberate choice. People claiming issues with stability or steering either are using a frame configuration completely unsuitable for luggage or have mechanical issues with the bike. Poorly adjusted bearing cones or improperly tensioned spokes will also make a bike feel squirrelly when loaded.