I think unless you use Swiftcast on Ruin III, it's best only aiming for one Fester in Dreadwyrm Trance. Even using 0 Festers in Dreadwyrm Trance is better than swapping in a Ruin II to fit 2 in.

R2 (DWT), R2 (3D + F), R3 x4, R2 (F +DF) ... F = 2536
R2 (DWT, 3D), R3 x5, R2 (DF) ... F ... F ... F = 2608
R2 (DWT, 3D), R3 x5, R2 (F + DF) ... F ... F = 2638
R2 (Swift + DWT), R3 (3D + F), R3 x4, R2 (F + DF) ... F = 2668