That's the whole point. Will it have enough capacity to be able to accommodate the 53/29 situation. We all know you should never find yourself in that combination but it's nice to know that if it did occur (forgetfulness, carelessness, etc) that it isn't going to rip your derailleur apart and break the hanger and end up destroying who knows what else in the process.
I have installed and ridden a drive chain combo that would not be recommended, but in order to accommodate certain situations temporarily I just used caution in the range that could have caused problems. But I would never run a combo that even allows the possibility of crossing the big ring with the big sprocket without enough capacity in both gain length and the derailleur.
The new 11speed derailleur has one cage than accommodate (providing chain length is correct) any combination of cassettes from 11/23 to 12/29 which is nice. The early generation 11speed derailleurs however require a slight modification and part swap to accommodate the 12/29. But the part is relatively cheap, like $15 or something.
But this thread is talking about 10speed capacity.

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My Colnago C59
My Special Colnago EPQ

Hi,



The Record 10S medium cage derrie should and will run any cassette from 29T down without a glitch running a standard 39/53 crank.

The long cage should take all available cogs. The main reason it isn't used much is that it is slightly slower in responding to gear changes and of course it is heavier and less stiff. Other than that it also requires a longer chain which once again adds weight.

Ciao,

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Being a snob is an expensive hobby.

yup, it appears you are correct. i just reread an old campy catalog and it seems that, many moons ago, i misread what they were saying.

Properly set up gears should be fine. I have never ripped a rear derailleur as a result with the big ring and the biggest rear cog. I have done this on 8 9 and 10 speed. I'm just stating my experience here. You do not need to do the same.

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I never took drugs to improve my performance at any time. I will be willing to stick my finger into a polygraph test if anyone with big media pull wants to take issue. If you buy a signed poster now it will not be tarnished later. --Graeme Obree

Durace but same concept on Wiggins bike

A 10 speed Shimano Dura Ace Di2 transmission with wide ratio cassette and longer cage rear mech for the mountains.

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I never took drugs to improve my performance at any time. I will be willing to stick my finger into a polygraph test if anyone with big media pull wants to take issue. If you buy a signed poster now it will not be tarnished later. --Graeme Obree