There is no really rule of thumb to guess at in tuning carbons.Is your bow 47# at your draw length or is it at 28"? If it is at 28" you would be pulling roughly 41# to 42#,that is light weight for a CE 250.But 250 I think are going to be too stiff for your bow,you may not have to cut them at all.I would start at full length and start adding weight from there to see how they shoot.I think a 150 would be stiff but a better choice to start with.It may be tedious to trim alittle at a time but that would be what is required to tune carbons and trimming carbons the spine increases more rapidly then a point weight change.I think with the weight you'll need to tune the 250's to a mid 40# bow you may end up with an arrow over 600 grs. without adding weight tubes.What size arrows are you shooting now?And what kind of bow do you have recurve or longbow?Is your bow cut to center or past also?