I have lightroom 5 on a 27 inch iMac and I am considering going to Lightroom 6. I currently have a 2.7 quad core processor and 16 gigs of ram along with a 512 mb graphics card. I notice that in Lightroom 6 a 1 gig graphics card is recommended. Would lightroom 6 run well on my computer or do I need a gig of video ram? Lightroom 5 and PS run fine on my computer with raw files from my Nikon D800 files.
Internet would show you comments from people using lightroom in tablets, many running Intel HD Graphics cards. I doubt those have anything close to 1GB in VRAM. I am unsure how does share RAM between CPU and GPU.
Anyway, Adobe has a list of non supported graphic cards: Adobe Photoshop Lightroom Help | Lightroom Graphics Processor Acceleration (GPU) Troubleshooting & FAQ
The application is supposed to test the card during the start up and disable the GPU features if the card is not appropiated. I have seen the warning mesage in photoshop, not yet in lightroom and can't say if performance really suffers.
So far I haven't notice a noticable performance increase. Maybe the day they support SLI...