XB500 and XB700 are similar but the sound is more rounded for the XB700. What I mean is that the mids and highs are a bit more upfront which means the bass is a tad bit less prominent. By standard though, the XB700 is not a "clean" sounding headphone and has plenty of coloration still. If you are a basshead looking for ridiculous, head smashing bass, the XB500 offers it more with the trade off of the mids and highs not being as clean due to the bass seeping into it. This can be somewhat rectified by equalizing. There are several threads here you can find for suggestions.
Overall I think the best value from price to performance is the XB500. I like it a lot and own a pair myself. As for XB700, I heard it in a store once so I may have a bit of the wrong idea on them since I didn't have anywhere near that much time on it. Spent maybe about a few minutes trying them out and testing things out. These are however my observation between the two. If your a basshead I strongly suggest the XB500 but if you don't want to sacrifice your mids and highs for that rattling bass, go for the XB700. The trade off in the end though is not as much bass though
ah okay thank you very much, but i will chose the 500, not necessarily for the bass (cause you told me that there is not so much difeerences), why, the xb500 cost 50$ less then the 700, so if i can save 50$ for almost the same sound ill do it, thank you again