The DMR tensioners are shit, they're plasticy and can't bit 1/8'' chains. Look into trials tensioners from trialtech, Try-All and tensile all make good ones. Make sure when your buying though that they mount straight to a derailleur hanger or bolt onto a standard wheel axle.
Link to a good trials store
That chart above is for XC bikes, you won't find many DJer's that run anything easier than 32-16. I run 32-14, but will soon be changing to 32-15 or 33-15. The trend now seems to be quite high, micro gearing. I've seen bikes with 25-10 or even higher. Which is pretty ridiculous on a 26''.
Another downside of micro gearing is that you get less mechanical advantage. The larger your chainring/rear cog the more chain wrap you get, which helps with acceleration. This is why race BMXer's run such large front/rear cogs.