Typically phototropic response peaks in the blue region and that, alone, is no reason for you to favor bluish light bulbs. See http://plantphys.info/plant_physiology/bluelight.shtml

I've had good results with 5000k T12 tubes when new but have to supplement with lower 3000-4100k as they age. I'm almost positive this is because the phosphors in the far red degrade quickly in the 5000k tubes. I'm also getting good results with 4100k T5s. This may be due to the higher amount of lumens T5s put out. The reason your seedlings are leaning may be due to the 6500k tubes putting out more lumens than the 3000k. I will continue to run a combination of both at 3/1-5000/3000.