Hmm, good point about Amarillo. I've only used it in combination with others in IPAs/PAs. Citra I've found to be very tropic/grapefruity. I thought Amarillo might be less so.
Regarding bittering, the LHBS guys basically say that bittering is bittering, that it doesn't matter too much what hop you use. I've always wondered about whether this was true. If it is, I guess I could finish off the Galena I have in the freezer to bitter, and use the Simcoe differently. Still need something to replace Amarillo - would prefer American strains, but might re-look at Willamette. I've heard Cluster described as "black currant" like which sounds fruit-like. I wonder how this might fit?