I've been playing for a little over 3 years now. I've seen the field distance steadily increase over that time. I could hit 300 within a couple months of throwing. After about 6 months, 350 was possible. Now I feel comfortable throwing mids up to 300 and teebirds/leopards to about 350 (meaning I think those numbers are repeatable for me.)
Today I was working in the field with Two Destroyers, a Wraith, a Beast, a Valk, two Katanas and an Avenger SS. It's quite a variety of discs, I know. Most throws were farther than 350 depending on the type of line.
With the understable discs I decided to try something. I wanted to bend my knees more and throw on a relatively high hyzer-flip line with the Beast and the Katanas. I focused on trying to drive with my back leg like a pitcher does in baseball. I crushed one of the Katanas to about 450 (according to Google earth). I have thrown them 420 in the past but this one was special. I don't know if I'll be able to do it again any time soon but if I do start hitting that kind of D consistently, I'm going to have to find a new field! I was also able to put the Valk to 410 and the Wraith/Destroyers (they're the same to me) to about 420 on flat lines with the lower, bent knee, leg drive approach.
Like I said I'm not sure I can repeat the 450 on demand but I feel confident going for 400 now.