Iphone 5 less storage for music?

I had an Iphone 4 and now have an Iphone 5. I just tried to sync to itunes with EXACTLY the same amount of stuff but says it will be near 3gb over capacity.
Music alone I'm near 500 songs less then I had before and 2 days worth.

Anyone got any ideas of why?

You've been syncing, right? Unless you set for manual management, iTunes may hold space on your iPhone - enough to put on it everything to be synced on your iTunes library. That's one if the reasons I don't sync music but rely on manual management - one of many.

In case your other memory is over a GB I'd clear out safari cookies and history. I'd also do a full shutdown and restart of your device.