Alright, yes, Cat 6a will support 10 gigabit networks, but right now your network most likely supports 1 gigabit speeds. 10Gbit is nice from a future perspective, but if your stations only need 1Gbit, then you can probably stick with Cat 5e for now.
My suggestion would be to get a company to validate the cable runs. Some companies have equipment that can test what speeds cable runs are rated for, the length of the run, and if there's any break points or interference. Testing out the wiring up front will save you many headaches down the road. After this is done, you will have a better understanding of whether or not it would be beneficial to redo the wiring now.
On a side-note, if you do need more bandwidth between your servers, then upgrading to 10Gbit within the stack (ie, just the server closet) may be beneficial. If this is the case, I'd also consider fiber cabling or Infiniband. Generally they'll cost you less for switching equipment and any server-only option won't require cable runs.