Samsung p7510 versus p5110 : what are the main differences?
P5110 is the Galaxy Tab 2 while P7510 is the original. The difference is that the newer ships with ICS and has a different SoC along with a slightly larger battery, while it is a lightly ticker. The P7510 came out almost a year ago.  

If you want future software upgrades the P5110 is a safer bet. See that datasheets for more info.