What's a 346?
A 340 is the high pressure 255 liter/hour. The 307 used to be the same as the 340 except for lower bypass pressure. The new 307 has a different armature and some other things. The flow charts are available on gnttype.org comparing the two.
If the 346 is not a 340 than I'd say go with the 307. It good for at least 550HP according to Joe and Harry at PTE. HTH,