[Sizzler]

Those rod ratio's are basically equivalent.
I'd choose a rod length based on the piston ring locations.

(throw+rod)
(2.125+6.8)=8.925
FE deck = 10.15 (or so)

10.15-8.925=1.225 for your ring package, which, in my opinion, is pushing things. Based on this, I'd go with the 6.7" rod if using the 4.25" crank.