[UK-CONTEST] Stacking toroids

[Chris G3SJJ]

I want to stack a couple of T300-2 toroids for a project I am working on. A couple of questions -

1 - Should each toroid be wrapped separately or should the non-painted side of each touch each other and then the whole unit wrapped?

2 - The finished component will be a 4:1 transformer to match a 160m inv-L. Currently I am using one core which already had 14 turns bifilar wound as 
4:1 balun but I have just altered the connections, so that one free end is grounded, the other free end goes to a series C and the centre tap goes to 
the Tx. It works well, tuning nicely with the C, although the core saturates at a specific power area, hence stacking. What are the relative merits 
are a straight winding against bifilar.

Chris G3SJJ