Hi Sebastian. When you say 5 months old and used stock, what does that mean? That the i5 has been on the shelf for 5 months, but has never been installed in a computer before? If so, that sounds like a great deal to me, although suspicious. The i5-6600 uses the same motherboard socket as the i3-6100. Be aware that the i5-6600 (non-K) isn't overclockable.