I split my tree because it was becoming unmanageable:-
1.Paternal grandfather and all his ancestors
2.Paternal grandmother
3.Maternal grandfather
4.Maternal grandmother
5 Wife's father and Wife's mother
(number 5 should have been split the same way, but it turned out that her mum and dad were related!)
It is quite easy to do using the All-In-One Tree, so first make sure you can view the All-In-One Tree. If your tree is too complicated, A-I-O Tree just hangs.
There is instructions here:
http://ftm.custhelp.com/cgi-bin/ftm.cfg/php/enduser/std_adp....I have a simplified version of this for FTM16, If you want it please send me a PM.