PHP Version

1) I currently have PHP Version 5.2.x for my site and thinking of upgrading to PHP Version 5.3.10
will I have any prob with the current up to date Version of Hikashop on my site.

2) Also, I noticed that I have the plugins; "User - HikaShop" and "HikaShop user synchronization", which look like they do the same thing, which one should I use?