They are different from sun bleached sagos because the fronds are variegated the entire time they exist, even when they are flushing from the caudex.
But I honestly think its difficult to actually tell them apart. I guess the variegated parts of a sago are more yellowish whereas a sunbleached sago has dry and white areas.
I dont think I would ever pay for a variegated sago. I personally dont think that many palms or cycads pull off the variegated look well (there are exceptions like some Licuala species and Rhapis).
-Alex

The different is that the variegated parts of the palm do not produce chlorophyll and are never green. Sun bleached palms or cycads will fade over time and the coloring is inconsistent; some parts are light green, some light yellow, some bright yellow fading through out the leaf. A variegated tree has sharp lines between the green and yellow/white and is very easy to tell it is variegated. Some even have lines down the petiole and trunk of the tree.

I am a variegated collector. You can see a large part of my collection on my site. I'll post a couple pics here to show you what I'm talking about.

Jerod

Here is a sago I have