If you are doing a super high end theater, then a cinemascope setup with a proper anamorphic lens on a motorized sled would be incredible. You want your 'prime' seating to be at about 3x the screen height.
Any number of manufacturers make scope screens, but if you are going with a fixed on-wall screen, then I would recommend the Carada Criterion in Brilliant White which is a top shelf screen for the money.
http://www.carada.com/ProductInfo.aspx?productid=PROJECTION-SCREEN-C136C
They should be able to make one the exact size you need.
Keep in mind that for a scope screen, the height will be about 70" or so at 17' wide.
Also, I would definitely get a masking system for the screen to ensure solid HD and scope viewing...
http://www.carada.com/Masquerade-Masking-System.aspx
The projector should be something bright enough to handle a screen that size, so probably something rated close to 3,000 pre-calibrated lumens would make sense...
http://www.projectorcentral.com/Digital_Projection-dVision_30_1080p_XC.htm
Digital Projection and Projection Design both have top shelf products which would meet the needs of a screen this large for under $10,000 for the projector.
At 70" screen height, prime seating is about 18' from the screen and that leaves plenty of room for at least a row in front and a row behind the primary seating position.
