Just to throw in my own observations after having used the trial version for about 2.5 weeks now: The library module is fine. Once the previews have been generated, everything is snappy enough. Switching to the develop module usually takes a few seconds when it's the first time after starting up the software; but after that, it's a relatively smooth transition (although sometimes switching back to library module is a bit choppy). In the develop module, things are generally okay, except in the following conditions: (a) heavy use of the brush tool and (b) working on high ISO images (i.e. in the range of 3200). I haven't done too, too much with the brush tool in LR4 yet, but I can say that, very reproducibly, as soon as I start working on a high ISO image, the program comes to a crawl - it's virtually unusable, and would be absolutely unusable in a situation where high productivity is needed. When I say that it comes to a crawl, I mean switching from image to image in the develop module, using pretty much any slider, zooming in and out, applying sharpening/NR, applying lens correction, using curves, etc. As soon as I switch back to a low ISO image (400 or lower), it's all good again. In the case of all images (regardless of ISO), sharpening/NR are much, much slower than they were in LR3.6. In LR3.6, switching on and off the "details" (using the toggle switch) results in an almost instantaneous change. In the case of LR4, it generally takes a good 5 seconds or so for the effect to kick in (making it very difficult to judge the before and after). BTW, all this was done on a fresh catalog, created in LR4. However, LR3.6 is also installed on my system, and I did have the LR4 beta on there as well (but I uninstalled this before installing the full trial version). In terms of my system specs: i7-950 OC'ed to ~3.4GHz; 12GB RAM (rated 1600MHz; set at 1500MHz); AMD Radeon HD6870; LR catalog and photos on caviar black 1TB; cache on a separate black caviar 1TB; LR itself installed on my C drive, which is a Vertex 2 120GB SSD; running two, sometimes three monitors (but LR only running on one, i.e. not using second or third monitor); Win7 x64 Camera specs: Canon 7D, using RAW files To be fair, another thing to point out is that it's not as if LR3 was always problem-free for me. Especially in earlier versions, it had it's slow moments (this problem seems to have improved in more recent version of LR3); but not nearly as bad as LR4 is. Hope this helps in terms of solving this issue, which is very significant for some.
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