Samuel L Jackson Dinky said:
Hi does anyone know the best video card performance-wise these days that can fit into an old Antec 300 case? Thanks!:D
Hi, suggest you post exactly that question over on the graphics/display forum. Not may people are checking this article to see new comments at this point.
Antec 300 is a mid tower case, and probably can fit just about any video card (a very long one might cause problems, but new cards tend to be shorter.)
Here is a list of video cards by performance: http://www.tomshardware.com/reviews/gpu-hierarchy,4388.html
If you give your rough price range people can suggest cards, or if you only want the 'best' then look at the top few cards and see if they fit.
As a starting point, 980 Ti, R9 Fury X, GTX 980, R9 Fury, GTX 970, R9 390X, R9 390 would likely all be viable.
Not knowing your background, it's possible you will need a new power supply when you upgrade video depending on what you currently have, and it's possible your CPU is not strong enough for cards as strong as the ones above to make sense unless you are planning to carry the video card forward into another build sometime in the future.