Posing with OpenGL preview will also be affected by a graphics card, since in that case it is the GPU doing the drawing in real time

I'm not very familiar with Mac hardware, but if I understand correctly, the G5 CPU came in many flavors. According to Wikipedia, in May 2005, the 1.8 Ghz was no longer sold, which would place your box at 4+ years old.You didn't say which variant you have. If you have the single-core SP unit, with the slower 600 Mhz front side bus, then you have a very slow machine indeed by today's standards.

However, if you're posing with OpenGL, then the GPU is the bigger issue. Wikipedia doesn't mention what sort of graphics processors came with those units, but given the time frame, I'd say they are not able to handle posing with half a million or so polygons in anything like real time, no matter how much RAM you add.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)