Lots of people out there have changed to a four spring set up on their pressure plates with no ill effects. There are companies out there that sell four spring slipper clutch set ups. I haven't ridden a bike with a four spring set up so I can't offer any comments on how they feel.
If you swap your slave cylinder out, you will have to choose between a 28mm or 30mm model. The 28mm will reduce lever effort by about 20% and will have a longer throw, that is, it will move the pressure plate further than the 30mm unit will. The 30mm unit should reduce effort more than does the 28mm model, but the throw will be shorter. I prefer the 28mm model.
If you go with the newest Brembo adjustable billet master cylinder, you'll be floored by how light the clutch pull will feel. going this route will probably set you back about $550-$600, but you'd have one slick feeling clutch and the improvement in the ability to modulate clutch engagement will blow you away even more than will the reduction in effort at the lever.