My opinion on the 5125's. For some stupid reason the 5125's and 5150's only have a 90 day warranty through bilstien. 5100 have limited lifetime.
One of my shock split a seal on me during a wheeling trip. Bilstien wouldn't warranty it because it was over 90 days. If it was a 5100 they said it would be no questions asked.
I really liked the Fox 2.0's I put on my dads k5. About the same price range as the bilstiens.