http://www.amd.com/us/products/notebook/graphics/ati-mobility-hd-5400/Pages/hd-5470-specs.aspx
3 gigapixels/s and 6 gigatexels/s. It seems to be realistic.
The new GPU-Z shows pretty high fillrates for Mobility Radeon HD 5470 (6 GPixels/s, 12 GTexels/s) that are higher than the fillrates of GeForce GT240 (4.4, 8.8 respectively). According to the PCMark 05 test, the actual fillrate is about 5.6 GTexels/s.