Have spotted some nice alloys but advertized as being off a mazda 6, will they fit on a mazda 5 or is their a difference? Sorry to ask but i know there are a few differences even on makes of car by the same manufacturer, thank you in advance )

 

You might want to post pics of the wheels in question, but that said, the bolt circle will be the same.... 5x114.3 (4.5".) The off-set will likely be different.
The Mazda5 uses the same offset as the Mazda3 which is +52.5mm.
The Mazda6 (first gen at least) uses a +60mm offset.
You may have to add some 5-10mm spacers in order to be good (have enough clearance) using the 6 wheels on your 5, which BTW is much easier than having too little offset.