I've been using it. Haven't done any really large levels with it yet, so i couldn't tell you about any speed issues. However, one of the new features of v4.0 is
Speed increases
Many optimisations have been made so that AC3D now loads, saves and edits larger models faster than ever before. AC3D continues to support unlimited numbers of polygons and objects.
So if Shambler has a version older than 4.0, his problem might've been fixed.
It's not the best program in the world. I chose it because I needed boolean operation, and it had it as well as a good balance between other features and price.
I did take a look at Quill3D and was impressed by what I saw if it. Would've bought that except that it only comes on CD and not as a download. I would need it shipped and unfortunately, with my work schedule, I'm not always around to recieve shipped packages, so I'd need to have it shipped to an alternate address so i'd have to pick it up which adds delay to getting the product... In other words, it would be a pain. My two prefered methods are download or buying from a nearby store.
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