Lowest X EP for C8.

Need to ask you Veterans who have been around the block a few times... What is the lowest recommmed power suitable for my Celestar C8? A meade 56mm. Plossl is 36x
A T Vue 55mm. Plossl is 37x
A GaryR 65mm. Plossl is 31x
Presently I have a 40mm. Scopetronix = about 51x
and a Apogee 30mm. Wide Scan II 84o AFV = 60x
I am looking for an EP that will capture the entire double cluster in Perseus.. so that it is framed by black sky. all I have been able to do is find myself in the midst of the Double.. any Ideas?? would a field flattener help.. JM

Thanks Bob & Hugh... I sold my 1.25" Celestron visual back & diagonal and invested in a new 2" visual back & 2" TV Everbrite Dia. also inserted a Skylight filter to keep the dust out when changing EPs in the field.. I like the idea of the Panoptic, my 22mm. Pan. let me view M-81 & 82 together in the same field with my 102 refractor.. I can only get one of the objects at a time with my C8. Should I invest in a 6.3 focal reducer, or just spend the $$ on a Pentax 40mm or the TV.Pan? Thanks (will be picking your brains with more questions I am sure).. jm