What is the hardware differences between Core and Core3 part from the CM?
Would it be better to by a Core to upgrade then?
The boards are basically the same. Main difference is, that the Core 3 comes with a passive heat sink, while the Core doesn`t have one.
Despite the fact, that upgrading the CM will result in a loss of warranty, the MAC-adress and serial number lasered onto the case won`t match the actual MAC-Adress and Serial number of the RevPi, since those data is saved on the CM.
So, upgrading the RevPi that is used live in production is something we wouldn`t recommend at all. For people using RevPi for testing, prototyping and so on.... it might be an option.
From an economic point of view: Buying a Core (to save 26 €) and upgrade it with a Core 3 Compute Module + a heat sink + glue (the CM3 alone costs approx. 25 EUR) ........ Not a good idea to save money.