Caryota is a large and unique genus of feather palms from southeast Asia and Australia.  They are unique first of all because they are monocarpic, meaning that each trunk flowers once at the end of its life and then dies; and secondly because they have bipinnately divided leaves, giving them a very distinctive look, different from other palms.  Some of them, such as 'king kong', can reach an incredible size, growing up to 100' tall with 30' long (or longer?) fronds.  Most are strictly tropical, but a few range into the mountains in Southeast Asia and have some cold hardiness.  Those that are cold hardy can grow well enough without a lot of summer heat.

My personal opinion is that C. maxima 'himalaya' and C. sp. 'solitare' are at best a long shot in the Pacific Northwest.  However, it must be considered that about any attempt is worth it when one considers what it would be like to have a large, bipinnate palm in one's garden.  I tend to think that C. sp. 'mystery' (I don't know where they come up with these cheesy names) is the best species to try in our climate: first of all, it may be just a little hardier, since it originates a little farther north than the others in the Himalayas, and also because it may be able to regrow after severe freezes because of its multi-trunked habit.  C. mitis, a tropical multi-trunked species, often grows back from the roots after a severe freeze in climates such as Florida: why shouldn't C. sp. 'mystery' do the same in our climate?  It is hardy enough for our mild winters and quite cool-tolerant.  It is also exciting to consider the possiblity of more Caryotas that may await discovery in the Himalayas and possibly other parts of southeast Asia.  One obscure reference mentions a species in Yunnan China.

Caryotas are reasonably easy to grow from seed, but initially slow.  They do not really take off until they have been established for a few years, and they like rich soil with lots of summer water.  I would strongly advise growing them on to a large size before planting out, and protecting them from cold for the first few years.  And I would probably not try them outside of the most sheltered microclimates, at least for the time being.

I would rank Caryota hardiness in our climate, again very roughly, as follows.  Again, these are guesses:

C. sp. 'mystery': -8°C/18°F
C. maxima 'himalaya' (formerly C. urens 'mountain form'): -7°C/19°F
C. sp. 'solitare': -6°C/21°F

The above three species may all be quite similar to each other in hardiness, and I am not at all certain they should be ranked in that order.  There are also:

C. ochlandra (considered to be very similar to C. maxima): -5°C/23°F
C. obtusa, 'Thai mountain giant', and the like: -4°C/25°F
C. 'king kong': -3°C/27°F
C. basconensis: -3°C/27°F