Glad you're going to take the precaution of doing the cloning before trying a regular install on your system. I think the free trial is on-going, so hopefully you won't have a problem getting the full 31 days.
I don't take any special steps to get really smooth playback in Edius. I don't disable LAN or my anti-virus (although I probably should, I suppose). Playback speeds are extremely good - not perfect, but close enough that I've never felt it was interfering in any way with the flow I get into when editing. At worst, there's a minor slow-down sometimes with titles, or (rarely) a dissolve. The system might hesitate a bit in the first play-through of a section of the timeline. From then on, it's smooth sailing through that part. You have a very powerful system. It's hard to imagine you'll have playback issues, but who knows? I'm curious to find out how it goes for you.
Until Vegas, I was mostly a Premiere guy. If any of these NLEs did everything I need, I'd be exclusive. I'm not naturally promiscuous.
I'm really comfortable in the Premiere interface, but they're married to CineForm for 3D editing, even in version 6 (the one that just came out). And for now Edius doesn't do Blu-ray 3D burns, and in my experiments I like how Vegas 11 deinterlaces better than Edius. To be fair, though, I haven't tried many options in Edius. It might well be that I simply haven't found the right settings for the cleanest 60i to 24p conversion. Regardless, though, I think I still prefer to maintain 60i all the way through the Edius process. I plan to render my projects to Canopus HQ Fine 60i 3D files. That way, I can keep the smoothness of 60i when they eventually get around to allowing us to burn AVCHD 3D 2.0 compliant Blu-ray discs. I hope we're not too far from that point.