I currently have a 2008 Duke that I use mainly as an alternate mode of transportation to and from work. I have a decent commute (35 miles one way) and the Duke is due for a new chain and sprocket. I'm debating on a 520 conversion kit but I would like some feedback if that is a good idea for a highway ride at 60-75 mph or even some suggestions on better gearing setups.

"Duke" or "SuperDuke"?

For freeway slogging - stay with stock gearing.

A 520 setup (which is the same pitch as the 525 kit, but narrower = lighter weight) of high quality kit, would be fine, almost regardless the application on a SuperDuke. Freeway commuting isn't a huge strain on chains and sprocket (unlike say stop-n-go urban or off/WFO/off of the track/racing).

Maximum longevity - part-for-part - will come from the heavier 525 setup. Frankly, if all you're doing is the slog - then the weight advantage of a 520 set up will do nothing for you.

I think sidewinder sprockets do a 520 conversion with titanium sprock with a life time guarantee.

what is the weight saving? and would a 520 haul my 100kg slim body without flying of the sprockets under heavy eccel who make the most robust 520?

I had already bought my stuff so I didn't make the purchase, but when my road bike needs a sproket, I'll try em out.
Lifetime warranty, you'll have to read if they do 525 Ti2, if they do, there's your weight saving with longevity.

http://sidewindersprockets.com/titanium ... ckets.html

Steel sprockets and a decent chain should get you 20k miles. 520 with aluminium will disintegrate in 10k.

See if you can get Viking to post in this thread. He has a 520 conversion on his bike.