Use either "shaded" mode instead of "Realistic" or turn on progressive refinement. The grainy transparency is a result of "Realistic" mode being essentially a progressive renderer, which refines the output over time/render passes. For editing and modelling it's best to work in "Shaded" mode, for lighting it's best to use…
Then try to assign a new material with low opacity, instead of using see-through. I don't have more ideas :/ Or maybe one more.Try to change the shading mode from realistic to shaded