there are changes to most burton models year to year. undoubtedly, the board's construction is drastically different for the 2014 model than the 06 - poppier, lighter, better construction etc. Not to mention if your board is beaten to shit, its also going to feel a whole lot different than a new 2014 board - lack of pop or flex.
as for what you wanna do, get more saddle time to figure things out. The custom is a all mtn board which will allow you to dabble in both.
On a side note, the cost of a popular used burton board such as the custom fetches such ridiculous prices that you can buy a brand new quality all mtn board from another lesser known manufacturer. just my 2c.