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Is it the future yet?
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I am needing a new 12-27 cassette and was thinking about the 7900 cassette.
Everything else is 6700.
Will it work?
Would I need the DA chain as well? Will that work with 6700 crank?

OR
Should I just go buy the Sram 1070.

Wheels are DA 7900 C-24's.
 

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1) 6700 cassettes are better bang/bux.

2) Shimano 10spd chain for 7900/6700 is directional; supposedly help with rear shifting, make it smooth. So pay attention if you get this chain. But I have used KMC gold chain (which is non-directional) with 7900 cassette and rear shifting is fine too.
 

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5700 cassette will also work fine and cost a fraction of the 7900. And last 2or 3 times as long.
 

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1. I would do a 6700 cassette, but there isn't a 12-27 ratio for some stupid reason.

2. So the 6700 rear derailleur will work ok with the 7900 cassette?
-I'm pretty sure there is a 12-27 105 version. I'd definitely do that before DA. It'll work as well and last longer. SRAM, Miche and IRD also make 10 speed cassettes that would work but I don't know if they have 12-27. I assume at least one of them does.

-yes, all levels of 10 speed shimano stuff works with other levels of 10 speed shimano stuff.
 

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So the 7900 cassette doesn't last as long?
That's correct. To shave a few grams off, the CS-7900 cassette has 3 or 4 (I can't remember exactly how many) titanium cogs. Titanium is good stuff. but is not very hard and no match for a steel chain grinding away at it. But people who use Dura-Ace cassettes generally don't care about durability. Their motivation is definitely something other than saving money.
 

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The theory behind making the largest 4 cogs titanium on 7900 is that typically it's the middle gears that wear out first. Since the large sprockets have more teeth and are used less, the titanium cogs should last as long as the smaller steel ones, giving you the same life as an all steel cassette. I have found this to work as advertised, although it gets a little trickier with DA9000 and Super Record where the largest six cogs are titanium.
 

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In terms of weight, you can save a few grams off with the DA, that's if you care about these things. However, as someone already mentioned, the price is very disproportionate on the DA compared to the ultegra. Ultegra to 105 price is much closer :)

With regards to the chain, I recommend you switch over to the Dura Ace. It just feels lighter than the Ultegra and shifts a bit better (might be placebo, although the 7900 is physically lighter). You have to take note that the 7900 chain is directional... meaning that there's a right way to install it.

Good luck!
 
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