Comfort is about equal, and of course highly subjective. Having owned current models of both Rangie and Cayenne Turbo over the last 10 years, I'd say the Rangie has it on "luxury" (cabin noise or overall NVH) and the Cayenne has it on handling and "feel" for the road, but if you want to drive quickly through twisting roads, both cars are enjoyable (even if the Cayenne has the upper hand.)
For quality and reliability, the Range Rover is notoriously unreliable, but in recent models (since it's basically a BMW) I found it to be far more reliable than prior decades when it really accumulated and earned the infamy.
For design, hands down, the Range Rover is a handsome vehicle, inside and out. The Cayenne in the latest 2011/2012 design is a bit ordinary to my eye and as far back as the 2005 model, the Cayenne lacked the distinctive visual appeal of what I'd expect from a Porsche -- expensive and just plain overpriced, if you don't place emphasis on the importance of sports sedan handling, the Cayenne is not justified for its price.
If speed is not important as you say, I'd hesitate to get the Cayenne Turbo, but I wouldn't necessarily buy any Cayenne except maybe the Hybrid, which is quite fun to drive and should retain resale value and long term appeal for not requiring such frequent trips to the cash-burning pump. Just the convenience of not having to waste time filling up is a significant plus, I find.
Thinking about cost again, the Range Rover will depreciate further and more quickly, so the total cost to own could be worse for the Rangie. I would encourage buying a one year-old example directly from a private seller to benefit from the first year depreciation cliff dive. In short, everyone cares about price when they finally realize the numbers!
If you're driving off-road or around town the Range Rover and its cameras and gadgets has an advantage, while the Cayenne is simply a tad smaller -- less space inside also translates into somewhat more maneuverable and car-like proportions outside.
If I were to buy a new SUV today, I'd get the 2013 Mercedes Benz GL350, hands down, the superior vehicle in all factors. Between Porsche and Land Rover, I'd take the Range Rover with no doubt.