The PowerColor radeon 7500 is almost identical to the ATi Radeon 7500. In fact ATi presently manufacturs PowerColor's boards before reselling them to PowerColor for re-labeling and resale.
The only functional difference is that PowerColor's Radeon 7500 is clocked at 270/230 while ATi's Retail Radeon 7500 is clocked at 290/230, and their OEM Radeon 7500 is clocked at 270/230.
Given that the R7500 is primarily memory bandwidth limited the real world performance difference is virtually nil.
The Radeon 7500 is also a very overclockable card.
The PowerColor model comes with 4ns DDR SDRAM, while ATi's own models come with 3.6-4ns DDR SDRAM.