As opposed to Boeing overpowering (see 757). Now Boeing are trying to replace that with 737-900X on ETOPS routes like YVR-HNL - good luck with that plan guys.
A342/3 were designed as frugal long range aircraft which made up time by not tech stopping. Bit of a hare and tortoise thing. Various threads here maintain 0.82-0.84 for 340 is a bit of a stretch in the real world.
The choice of CFM56 was either economic or franconomics (Snecma being a partner in CFM). The aforementioned RR 757 engines were probably a better fit (RB211-535C say) for power - especially with Trent 500s being the powerplant for the 345/6.