If a user answers a discussion with possibly 75 replies, and its set for 20 per page, making the thread appear as 4 pages to that user.

When they reply, the redirects them to the first page.  They then have to click PAGE 4, to see their reply.

It pisses users off.

I have tried to fix this, which if I set in the MYSETTINGS to NEWEST FIRST, it places the newest discussion on PAGE 1 at the top, which makes sense, and works fine, but most people dont read that way.

They dont start reading a discussion from PAGE 4 and work their way backwards.

So my question is, how can I get the postback, after a user submits a reply, to redirect to that last reply page, which in this case would be 4?

Have you searched the forums. This has been debated a lot in the past. I don't remember whether this was resolved though.

I found a few topics on this, but nothing looks to be concrete that a solution was developed.