Hi Micawbbr,
Many thoughts come to mind when considering EO vs FO: cost vs lasting power, irritation with some EO's- clove is an irritant to some, bergomot others (must use begaptene free berg eo). Another is some eo like smells can be made into fo's since they are just better with regards to staying power and lasting through CP rigors-heat, alkalinity, etc. A good example of FO designed to smell like an eo is Cedarwood Mint (YUM!), English Lavender (the eo is very faint in CP soaps no matter how much you use but the FO is a very nice & rugged duplication), Frankincense & Myrhh (have not found a good FO duplication to measure up the $$ eo's but I know Zum bars use a FO- see label).
Do the math to get an idea of cost comparisons. Try patchouli eo since this always smells great. Use a tiny amount since it survives well in CP soaps and stays. On the shelf, the eo ages beautifully, gets mellow and more like a loving hug. I love patch + bitter orange eo's in melt n pour, but alas, the citrus gets wiped out by the lye in CP. I think you'll find, like many of us, experimenting with both is fun.
Best,
Julie