Do you really have to use TG Classic? TG2 is really much better. TG Classic really has a lot of limitations especially on the Mac:
- It's not Intel native so it's running under Rosetta and not reaching its potential full speed (TG2 is Universal, so Intel native)
- It can only use one core (TG2 can use all your cores)
- It's limited to a maximum of 4 GB of RAM, although I'm not sure there's much you could do except render huge images where that was likely to be a problem (TG2 is 64 bit)
I don't think there's much you can do to optimise renders. You can probably set the buffer size quite large without problems, set it to 128 MB or something. I'm not sure if it will make much difference. It's really the only "optimising" setting you can change.
If you find TG2 harder to use, and really it isn't as easy to get to grips with as Classic, it might help to know that there are a lot similarities between the two. You can actually make scenes in TG2 in a similar manner to how you'd do it in Classic. I think the key is to ignore the Network view, you don't have to use it. Surface mapping is really very similar, a lot of concepts from Classic carry over to TG2. It's just as easy to add clouds for example.
I have been working on-and-off on a transition guide for Classic users to move to TG2. Would this be useful to you?