I like getting females in the 800-1000g range for a few reasons.
1. Since they arent breeding size yet, theres absolutely no temptation to shorted quarantine to get that lock youre just dying for. At the end of 6 months they should be about perfect size.
2. Youre still getting a good size girl, but you there can be a decent price jump between "proven" and females who havent bred yet.
3. Youre still saving a year or so in feeders/housing/time...worth the price difference to me.
Just what works for me. Ive bought females from 60g-3500g but 800-1000g seems to work the best for me when they are available.