when it comes to the 6.1....i was talking to Dt swiss rep, he told me and i quote " the 5.1 are were designed and made for race use only, it is a known fact that racers change the rims after everyrace because the rim is so soft" then he went on saying "the purpose of the rim is to limit the amount of pinch flats by its shape and structure, NOT to be used by general consumers unless they plan on building new wheels constantly"
i've seen it, i've lived it...but i dont know about the 5.1 though
I have read many reviews on the 5.1's and the issue of "soft" always seems to come up. Some contend it was an issue w/ the 6.1 or different model years. Others state they have been on their 5.1's for seasons w/o any dinging / denting. Regardless of optomistic thinking , in the back of my mind, I see "soft'. On the other hand the I have had many Mavic rims that have held up nicely from trail to DH use.
I would go with Mavic. Over the 10-15 years that I've had Mavic rims I have never had any bad things to say about them.
I bought an Industry 9 wheelset with DT 6.1's at the very end of June and hated them so much that I spent almost another $250 to replace them with Mavic 823's 1 month later and tossed the 6.1's into the trash. The rims were junk in every way and were so damn tight that I also ruined a pair of Michelin DH 16 2.5's.
Now to be fair, I've heard people actually like the 5.1's so they may be designed/built much better. I would still never buy one and to be honest, I would trust a pair of Mavic 819 tubeless rims over the DT 5.1's.
Don't buy the BS about the soft metal preventing flats. It's still metal and it's still a helluva lot tougher than rubber. I didn't get any less flats on my 6.1's than I did on the 321's that I had been running for nearly 7 years (and they are still in good shape). The DT wheels may be lighter than the Mavic 823's but a flat tire is going to make much more of a difference than 100 grams.