Thanks to the fantastic generosity of Michael.T (
http://www.curry-recipes.co.uk/curry/index.php?topic=7896.0) I at last have my hands on some of the coveted commercial Rajah Premium Madras powder, so thought I'd do a side by side comparison to see how it stacks up against its domestic market counterpart, Rajah Mild Madras powder.
In the picture below the Rajah Premium is on the right:

As you can see, the Rajah Premium is a little darker and not so yellow as the standard powder, which could indicate less turmeric and/or a little more cumin or other darker spices in the mix.
Taste wise there's definitely a difference.
The Rajah Premium has a less harsh, more rounded, balanced and 'sweeter' taste. In fact I found it quite moreish, and went in for a fair few finger dabs.
Heat levels are identical.
It's not life changing, nor is it going to magically transform your dishes and take them to a new stratospheric level, but given the choice the Rajah Premium is the one I'd go for every time.