The OP has specified SFP+ switches. And it's a building to building link. Why would you not use an optical fibre? A pair of 10GbE LC adapters is about £35 if you buy the Mikrotik ones and a pre-made fibre cable is £10-£20 depending in the length. To go 10GBaseT with a CAT6(A) cable would be £45 each end for the SFP+ adapters at least and limit the OP to 10GbE. It doesn't make sense financially, it doesn't make sense from a performance perspective, potentially (but very unlikely) there could be earthing issues between the buildings and there is nothing as future-proof as a fibre. It's just the right way to do this.