I bought it but did not measured it... at the end it is just a 10cm difference... I think that there is plenty of cable that should be enough for any road bike, but cannot tell if it is enough for tandems... You may try to measure your bike to see if that difference is relevant...

Unless you need to rig the rear of a tandem there is no issue. I have a 66cm road bike and the cables are always plenty long enough. Hope this helps.

1700 length.

Just single ended - I purchased mine for a Shimano RSX shifter and the ends were a perfect fit without the need to trim off the unwanted end!

No, only a road type end (ie no good for older bmx-mtb type brake levers)

no they have one end with the appropriate nipple and other end bare.

Yes

I see no reason why they cant be used with Rival. Why not try the transfil cables. They are much cheaper.

Yes, definitely

Check to see if the binding plate on the calipers is clean and binding (sound like its not seating correctly). Check how tightly you are doing up the bolt. In my experience these cables work with Shimano brakes quite well. If all else fails, flip the binding plate so that the cable is being clamped with a flat part of the plate. If this doesnt work, insert a thin flat washer between the binding plate and the groove in the caliper to get better crush on the cable. Hope this helps.