Back when I used my yellow XL-5 I ran a Orion Formula Pro BB Modified 15T Double in my Rustler with good results. I believe that all the Formula Pro motors have adjustable timing while some of cheaper Method motors have fixed timing, also the Pro BB has ball bearing instead of bushings.
Seeing as how the Orion Formula Pro BB now seem to cost $50 to $60, only paid $35 for mine in 08, I don't think it is worth the cost now at the current price.
Any rebuild-able 540 mod motor will probably last longer than a Titan with proper maintenance, and most any 15 turn mod motor should out perform a Titan.