Canon ? Full frame or ultra wide lens for 1.6 crop?

I've had a 40D now for a few years and have tried to get out with it as much as I can. I would say that my passion for it has only increased as my shots have improved. I now mostly enjoy travel photography but shoot a lot of family portraits some landscape and sports as well.

On a recent trip I borrowed a friend's 5D and really loved using my 17-40 for ultra wide angle stuff.

Now that I returned his camera I find myself scratching my head and considering getting a Tonika 11-16 or should I just stick with lenses that are will work on both crop and full frame and instead use the $700 bucks on a used 5D???

Thanks for any insight...