Fitting clinchers to Mavic Ksyrium Elite?

I used 28mm continental 4 seasons on my elites in winter.
Didn't have an issue fitting them.
Those wheels didn't last long in winter though.

I have a set of Ksyrium Elites, it is a bugger to get just about all clinchers I've tried onto them, if you can get one side of the tyre over the rim, the trick is to fold the other side of the tyre towards the rim, and use your full body weight to get it over as you sink down onto it. The last couple of mm of tyre are particularly tough, but if you position a couple of levers strategically, and really force your arms down, you should get somewhere.

I've got Kysrium Elites.

 I use 25's not 28's, but had no trouble fitting the updated Mavic Yksion Pro UST's (the new model is significantly easier to fit than the old ones). These ride beautifully, but wear quickly and puncture easily. 

I have just fitted Schwalbe Pro One Microskin TL Easy on both wheels. The front went on a few weeks back. I almost broke a tyre lever getting it on and needed co2 to seat it. The back went on yesterday, rolled on easily with just my thumbs and seated in seconds with a track pump... Not sure if this is due to manufacturing tolerances or improvements in my technique! I have heard the updated Pro One TLE are even easier.

I found you really need to keep the bead in the dip at the centre of the rim at all times, and finish at the valve (where it fills the dip).

Good luck!