Yes you do swim faster...YOU HOLD WATER on steroids and your body is 50-65% WATER!!!!!!! Do the Math!
STAY POSITIVE!!!!!!!
Yes but steroids also increase muscularity and reduce subcutaneous fat. Contracting muscle is denser than water and causes you to lose buoyancy; fat is less dense than water and increases you buoyancy.
Being a large mass of twitching muscle is hugely disadvantageous to a swimmer (especially in swim events over 100m). However, the increased recovery and capacity to train at a higher intensity from using steroids are so great that it would probably override these negative effects and give the user a competitive advantage.
The guys in the pictures are carrying more muscle mass than is necessary however.