Party - the 3% variation was the power given to the Scottish Assembly on formation. Never used as too much of a political hand-grenade until the SNP established a fiefdom.
The new powers come into force now (Scottish Act) and allow them to set any rate of tax (although basic rate threshold still set by UK gov). It is now a balance of "what do we need" (reduced income from UK tax coffers) vs "what can we get away with grabbing before losing votes". When you look at the SNP voting demographic, you can see the obvious targets are those in the 40% bracket.... After all, most of the really wealthy SNP supporters live outside of the UK (Sean Connery, Billy Connelly etc. etc.)