Rhett Butler's People is a lot more true to the characters than Scarlett, but the plot has a lot of conflicts with Scarlett so I would suggest letting yourself forget about Scarlett before trying Rhett Butler's People. That book also focuses a lot more on the setting and the events of the time than on Rhett himself. GWTW was very focused on Scarlett herself. RB'sP will either make Rhett more human and appealing, or kill the 'mystery' surrounding him, one or the other.
Well said, anon. Thank you! Hope this helps the earlier anon a bit more than my half-hearted answer =)