What browser feature would be good to discern a mobile browser able to handle js well from one that doesn't?

I have been testing our mobile site on an android and iphone and feel that I have a good working website for those browsers. The problem is that I just got my hands on a blackberry 5 and the results are pretty appallingly bad. We are using jquery and it takes 20+ seconds for the js to load get itself oriented.

My thought is that we probably are just better off 开发者_开发百科removing or severely curtailing our use of js on a browser like BlackBerry 5 or lower which takes me down the path of browser detection.

I have used modernizr for this project and I'm wondering if there is a particular feature or set of features that we could detect and that would then allow me to divide the browser into groups of Excellent, Good, Medium, and Poor as found in the Quirks Mode Browser listing found below. Alternatively, I would settle for an answer divides it into excellent and everything else.

http://quirksmode.org/mobile/mobilemarket.html

Based on the data presented here. http://www.w3.org/2010/01/results-wctmb2

It appears that two features of browsers that effectively separate high levels of js support from low levels of js support are support for localStorage and support for canvas.

Every browser at or below 50% fails to support either localStorage or Canvas and every browser above 50% (except for a couple versions of Firefox and Fennec) support both.