I think you will compare anyway regardless of the testing. It's hard not to.

We decided to test. If anything it helped us to compare them less. There were some expected results (DS5 doing better in reading, DS7 better in spelling), there was also a surprising part which showed that DS5 math abilities are very comparable to DS7 math abilities.

If you can afford the testing then I say go for it or you will always wonder.

LMom