I once had some commercial equipment removed from a cafeteria. After seeing the 1/4-3/8 inch thick grease buildup on the sides of the fryer, my appetite for fried foods disappeared for a time. We actually started by scraping with a 2 inch putty knife. Then, we tried everything we could find. For places you could cover, we sprayed with oven cleaner and covered with plastic which was the method used for the company's candy production equipment. They sprayed everything on Friday night and let it sit for the weekend and cleaned it on Monday. The best product I have ever found was "grease control" from the Odo-ban company which is actually an emulsifier so much more green than the toxic chemicals found in some of the cleaners.

Effectiveness is influenced by capacity of unit. If you are trying to mount a 270 cfm fan more than 30" above cooktop, then it may make noise but will do little to clear the air. If it is 1000 cfm, then it can be higher than 30". So the answer is "it depends". Most people don't mount them more than 36" above the cooktop unless it is a really high powered unit.

If you love the marble tile, go for it! You can always buy a stainless or white range hood backsplash like this http://www.wayfair.com/Air-King-Range-Hood-Back-Splash-SP2430-AXK1174.html to slip in place when you are cooking something really messy. I have a travertine backsplash and use a stainless sheet when frying. It works great and no worries about stains ruining the stone.

I wanted to use a shimmery pearl backsplash but it was problematic to install. Looking for something reflective. My island is deep blue (sea serpent by Sherwin-Williams), cabinets white with clear glass in second row uppers, fixtures, pulls and knobs all champagne bronze. Hoped to find something more exciting than white subway but I need help and fast so we can install the range hood and the stove!