January 06, 2013, 01:19:17 am
Its a bit like the difference between an older 480 and any of the 5 series up to the 580. Although the 480 is basically lower spec, less cores it was a powerhouse and out performed most 5 series. Why? Not sure, but as I couldn't get supply from my regular hardware seller I opted for a 560 and should have gone with the 480 and sourced elsewhere. Anyway.
Some things that might be different for your cards:
1. are they the same make? there is definitely a lot of difference between producers, both in quality of chips, overall speeds (mainly bus)
2. are they set to factory defaults or was the 580 boosted and currently the 680 is not?
3. even though the 680 has 3 times the CUDA cores than the 580 and better clock speeds, the bandwidth is better on the 580, and this could explain the real-time FPS difference and why renders are much the same (same due to Lumion, other PC specs and DX9)
4. texture fill-rate is quite a critical and the 680 is definitely much better so its likely limitations of other parts
5. are you running screen at same resolution
6. your PC specs may be that its not able to make any further use of the 680 over the 580 anyway,
7. when you get down to a few FPS in real-time its not really anything and more to do (IMHO) with Lumion and general PC specs etc. My 560 is OK with small to some larger scenes, but chokes on anything too much and real-time FPS dies, but the scenes still seem to render in roughly the same time (+/-).
It's render time that of course is the time cost to you, if you are finding you need more FPS in Build then just lower your Editor quality and even resolution % to help in the build phase.
The advantage you have with the 680 is an extra 1GB of VRAM which helps with allowing such a heavy scene to be loaded and the cards ability to handle higher display resolutions.
It would definitely be nice to see a good render improvement for the 680 especially with 3X cores, but as Michael mentioned its likely GPU drivers for DX9 (although some things in DX9 are still or just as fast than in DX11), and the real-time technology in the background of Lumion compared to something like Crytek or Unreal.
You could test your GPU with some of the benchmark tools such as Furmark etc found at geeks3d.com (see also links mentioned in forum) and see how well your card compares.
Appreciate your post. It is interesting to hear your story as have been struggling with my own 560 card an whether to upgrade or not.