Here's some options from your description:
I'd look into the BCC's if you favor bright red tails. They usually hold them through their entire lives, and I've seen some with bright red to deep crimson tails that are very stunning. I personally favor the Peruvians but they can be speckly, but Guyanas and Surinames seem to usually be a little "cleaner". Here's a great link to those different locales: http://www.riobravoreptiles.com/index_livestocksite.htm
BCCs do tend to become larger than BCIs, so I would look into a male over a female.
The other option I can think of is Colombian BCI boas, where females can get in the range you specified (males usually smaller, 5-7 ft but there's always exceptions of course). Most regular Colombians will start with bright tails but will usually fad over time. For speckles, pastel Colombians are very clean and some hypos/super hypos too (my hypo girl is very peppered, so of course it depends on the individual). The ghost or anery morph Colombians (just a couple examples) don't have the red/orange tails, but they are stunning themselves.
Here's a great link to some more boa morphs that you can look into: http://www.classreptilia.com/boa_morphs.htm
and http://www.blumenboas.com/boamorphs.htm
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