Is the 6950 the true replacement for the 5870?
And even then the 6970 is only 10-15% faster than the 5870.
Yup most non tessellation games only saw around 10% increase from 5870-6970. Besides some of performance are from the increased core and memory clocks. Same with 6870 they clock it to the moon to make up for the reduced shaders in the end it can barely outperform (~5%) a 5850. I think the 6 series are the most unimpressive series from AMD in terms of performance jump.
They didn't need to do much because competition didn't bring that much more.
Is the 6950 the true replacement for the 5870?
I've got a 6870. I can return it and get a XFX dual fan 6950 for about $30 more.
No and neither is the 6970. A 'true' replacement for the 5870 will be HD7970.
I would do it. 20% more performance for only $30 more.