Back in the day, the 735 mm RooX Torque Bar used to be the widest and it also got lifetime warranty. An amazing bar that I still miss, but not exactly for a P20 Ritchey, if you ask me.
On the other hand, FUNN were doing as recent as 2008 a pretty low rise 750 mm Full On bar that Sam Hill was sporting on his Iron Horse Sunday. You might want to check that out and give it a try. I also find the 710 mm Race Face Air Alloy riser that I currently use on my Jekyll to be wide enough for XC and besides that I have a 720 mm Renthal Jump Bar on my MaxMax dirtjumping bike that I absolutely love.
1990 GT Karakoram 20" Purple Haze (urban project); 1993 GT Karakoram 20" Ferrari Red (classy beater); 1993 GT Karakoram 14.5" Black Light (almost original); 1994 Breezer Jet Stream 18" (unlikely story); 1995 Winora full suspension (a fine riding mistery); 1997 Kona A'Ha (anniversary edition); 1997 GT Arrowhead 18" (poisoned gift); 1998 Stevens 6.1.2 (true warrior); 1998 GT Moto cruiser (just google it!); 1999 Santa Cruz Chameleon (the heartbreaker revived); 1999 GT Lobo 1000 (retired with works Super T); 2000 GT Lobo (turns original); 2001 Klein Attitude Comp 19" (ultralight project); 2001 Cannondale Jekyll 1000 SL (better that a lot of "fresh" bikes); 2003 Intense Tazer (close to factory team spec); 2003 Intense M1 (old dream on hold); 2007 Crupi Pro XXL (pumptrack teacher)