So I'm an idiot and bought the wrong size...

To be honest I dont feel like I can ride aggressively on the bike, comfortable flowing but not chopping and changing direction. Most of my riding in the past has been single track on a light, compact XC hartail so I am used to a nimble feeling bike ( i know an XC bike is miles away) Most everything is pointing towards fairly strongly that I bought wrong!

Yeah, does sound likea 54 would be better. If it feels a tad short you can increase your stem length a fair bit to compensate. 70mm is pretty darn short (IMHO) so I certainly would'nt want to keep the 56 and get a shorter stem, if I felt streatched.