In water, all those ppm are floating around waiting for the roots to snag them when they want. In dirt they have to work for it.
Not sure what you are using for nutes (didn't read back to see if you posted) but 450-500ppm is what my ammended RO water has in it. calmag, silica, etc. not food. If you had 150-250ppm of calmag, that doesn't leave much food in 470ppm.
FWIW I have run-off on the 2000-3000 range regularly (sometimes in the 4000s) but I am using a dry top-feed that is organic, so it's a little more forgiving than salt-based nutes.
If you are just shifting to soil forget the super-anal DWC ppm stuff - this is way easier. Watch the plants, and follow the directions on the nutes for ammount, not worrying about ppm. Somewhere between a quarter and a half of what is recommended is going to be safe without overfeeding. Mix it up, then see what ppm you get if you need a ballpark figure. It'll be different for every brand on what they recommend. It may take a few grows to get dialed in, but it's worth it to sort out what works for you with the stuff you are using.