Bjorn3D posted a review on the PowerColor X1600 PRO AGP 512MB video card:

There is still need for AGP cards. A lot of my friends are using older systems and don't think of migrating to PCI-e camp just yet. There is a good reason for that since latest AGP boards still perform pretty well. However, it's a pitty ATI hasn't decided to use a bridge chip on one or two high-end cards like X1800 or X1900. This is where NVIDIA gets the kudos. They have a broader AGP line of products being served to its customers. ATI fans have to live with last year's high-end parts like RADEON X850 and X800 GTO.

As for our PowerColor X1600 PRO AGP model with 512 MB framebuffer it's not up to X1600 XT toes, but it's not weak either. It's a good solution if you don't want X1300 and want to go with something stronger. Performance wise it does its job, but I'm afraid more memory won't necessarily help in most applications. There are other limiting factors that come in to play such as low memory clocks, cut down shader engine, less vertex pipelines or 128-bit bus. If you're upgrading from let's say mid level RADEON 9xxx series this move will be well worth it, especially in games where latest shader technology is used and the user will notice benefits.