I don't know if it works for you in vivo, but in vitro a second antibody (Fab2 fragment) crosslinking the anti-CD40 tremenously boosted the effect as compared to CD40 alone. But that was for human monocyte derived DCs, probably worth a try in the mouse?

I have had good experience with FGK45, which stimulates murine B cells and DC in vitro. 1C10 is practically the same (we have sequenced VH/VL regions in both FGK45 and 1C10). I have not compared them or others, though.

I agree with Gernot Posselt that using a bivalent fragment will rule out FcgR interactions but interestingly in the mouse a cooperation between FcgRIIb and agonistic CD40 effects have been observed in vitro (see J Immunol-2011-White-1101135).

Thank you for all the advice!