If you feel the DGs are heavy you are gonna think the same with project X

DG S300 are 130g or 132 with Sensicore. PX 6.0/6.5 are 125g so will feel a bit lighter. IMO, I would go for PX 6.0 and try them, if they feel too soft then hard step them once. They are stiff to flex anyway. PX 6.5 are for gorillas mostly and will limit you on feel shots. I tried them once and got rid quick. If you are going with PX flighted then they are softer than std PX and not as good IMO.

I have just swopped from dg400's to project x 6.5, i love them they feel much lighter than the 400's and my iron play has never been so accurate.