Is "tes res" maximum texture size?   There can't be many textures that require, or are even grateful for, a size of 4096, I suspect.    I don't know how exactly that setting impacts CPU or memory, but, if there really are textures that size being loaded, you could probably reduce their size substantially and still have a very fine result.   

Reducing the bucket size often does allow a render to complete, more slowly, when it won't complete at all with a larger bucket-size defined.   Poser is supposed to reduce the bucket automatically, if the complexity of the rendering calculations is going to overwhelm the system resources.   That does happen, but I believe it happens more reliably at Poser 7.

I use pjz99's technique for freeing storage quite a lot.   With Poser 6,  you need to follow svdl's remarks:  there can never be anything north of 2Gb of memory in action and quite a lot of those 2Gb will always be taken by those annoying programmes that insist on scanning each other all day long.   I tend to minimise Poser well before it reaches 1Gb, but it doesn't always work, because the scene won't always return when it is maximised.   There will always be a delay before Poser draws the current state of the render, though, so don't despair, if you initially see a blank scene and a "Not Responding" flag in the window.

As far as Carrara is concerned, Poser 7 can't import directly to Carrara.   Poser 6 can handle just about anything that comes out of Poser 7 and Carrara 5 can handle most output from Poser 6.    If Carrara is your intended final render engine, though, don't waste time in developing elaborate materials in Poser (any release), because Carrara can't handle them.   Its own texture engine is very sophisticated, so anything Poser can do, I'd guess, Carrara can also do, but you need to work out how to achieve the same effect all over again.