After many of you pointed out that the true comparison between the bases would really have to use a Madras recipe in order to be fair to the Darth base, (since this is the kind of curry for which it was intended) I defrosted some more base sauce and went to work. I didn't take so many photos but you get the point.
Here are the resultant curries (both curries on both plates, Saffron at the top, Darth at the bottom). I thought I'd keep things simple and so opted for the Rajver Madras recipe, which can be found here
http://www.curry-recipes.co.uk/curry/index.php/topic,2152.0.html The results were astounding.

So, for the Bhunas, Saffron was the clear winner, getting a unanimous thumbs up from both my girlfriend and I.
This time however, it was an altogether closer race. With the Bhunas I explained that the curries were very different. Well guess what! With the Madras, they were
very very similar, to the point that I didn't have a preference - they were both absolutely delicious. Lashings of beautiful sauce that I happily mopped up with some garlic and coriander nan from the corner shop

My girlfriend agreed that they were very similar but decided that she preferred the Saffron base as it was more "Tomatoey", which she liked.
So, overall, it's still a win for Saffron but the Darth base does really come into its own far more when used with a Madras type recipe. However, Saffron still beat the Darth base at its own game (only just) and offers far more versatility.
In conclusion, the Saffron base is as good or better than the Darth base at making Madras style recipes. It is better at making Bhuna type recipes, and is a proven winner for Kormas, Jalfrezis etc. etc.
Darth's Madras base is a really tasty base and great one to try but as far as bases go, I think I know the winner ;D