Talk to a powder coating shop about having them degrease it. A friend of mine did that and said it was well worth it. They tanked the whole frame in phosphate or something like that and it removed it all. In my little experience it takes to darn long with the sandblaster and is a waste of time.
I like the oil eater they sell at Costco myself, its like 9$ a gallon as concentrate and I use it as is. Spray the hell out of it, let it soak awhile and pressure wash it and most of the grime falls off in chunks. Rinse and repeat! Good luck.
