Well, a lot of questions that can cause flaming discussions. I personally find it more stable than the PC version seems to be - never had an oom error on Mac.

Poser import works fine, some minor issues at the moment because Poser 7 writes non correct path names into pz3 files. But this is something that I expect to be sorted out soon, either from e-Frontier or from e-on.

You have an eMac? Well, not the fastest machine available I would say. But it should be possible to run Vue on that. Even when the generation 6 is Universal Binary and runs on Intel Macs a lot faster. Maybe time for a Mac  Mini?

Best proposition maybe is that you download a demo of Vue 5 Infinite and see how it feels for you - on your machine. Then you can decide what to do. Even when V5I of course does not have those fantastic volumetric clouds you maybe want.

One day your ship comes in - but you're at the airport.