Thea Render is one of the few commercial renderers that can offer both biased and unbiased render engines. Biased/unbiased is a question about accuracy of render algorithm, biased rendering do make some shortcuts for faster results that are needed for animations and so. With it user has a control on every aspect and parameter of render engines. Unbiased rendering is progressive by it's nature, it does offer a easy, parameter free and highly accurate, but slower rendering. You can use the same scene no matter witch engine you choose to use.
Thea and SU both do use OpenGL for displaying the workspace, so one can say that even reasonable "light" GPU can handle the burden (even integrated display adapter might be enough). Later Thea will have GPU accelerated rendering, but at the moment just your system should work just fine with Thea. With i7 and 16 GB RAM it's hard to choke Thea as it does benefit from 64-bit OS - you can render more complex scenes and use more freely some features like relight (as available RAM is the main limiter).
You can freely test Thea, with resolution limited and watermarked version. If you want to compare render time for 720p or higher, it will raise linearly related resolution change. So even with a smaller test render you can estimate how long it would take to render some higher resolution image...
Please, be free to join to Thea Render forums for further questions.
ps here is some interesting music & relight experiments by Wax http://www.youtube.com/user/wax78/videos?query=relight
