If Apple update the Mac Pro this year, there's a very good chance that as well as introducing faster CPUs, they'll offer faster graphics cards. The FirePro D300, D500 and D700 in last year's Mac Pro are manufactured by AMD. AMD have spent the last few months updating the FirePro cards they make for PCs. The specifications of these new cards show how much more AMD can do for the same money.
The cards in the MacPro are custom made for Apple, but there are some rough equivalents between the D-series and the PC W-series. For example the D300 has similar specifications to the W7000.
The W7000, W8000 and W9000 first appeared in 2012. The PC equivalents of the D300, D500 and D700. This year Apple may base their new Mac Pro GPU cards on more recent AMD cards.
Here is a table edited together from tables on the AnandTech site. The table is divided into three groups - representing low-, medium- and high-end Mac Pro options. Each group shows the original AMD card, the Apple-specified Mac Pro card and the 2014 update of the 2012 PC card.
At each level AMD have at least doubled the VRAM, added 40% more stream processors. The W8100 and W9100 have wider memory buses (so more information can be transferred for each command) and many more transistors.
Although Apple can specify any number of stream processors, clock speeds or VRAM, these more recent cards show what AMD considers is the low-, medium- and high-end when it comes to PCs. For Mac owners perspective, they show how much card for a similar amount of money AMD can now make compared with the cards in the Mac Pro and 2012.