Hey Adrian :
i5 6600k is on sale for 209$ and regular i5 6500 is 201$. should i get the i5 6600k for future proofing? the board i plan on using is the msi h110m pro-vd
If you think you will still be using the 6600k when you buy an MB to OC it I would.
If you already have a cooler that will work with it I think you should.
If you don't have a cooler for it or plan on getting an MB to OC in its lifespan I don't Think it is worth it.