You can use .11 for standard tuning. Stevie Ray Vaughan used to play on as high as .13 (though he played in Eb). .11 is suitable for downtuning too.
I wouldnt go further than a half step down from E standard. Thats me tho. Buy a set and experiment. They're only $6 dude.
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i've gone down to Db with no issues. Any lower and you'll want to go up to 12s or higher
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Also depends on your guitar's scale. On 25.5 you can definitely get to D standard or below. On a 24" scale guitar, it won't really go below Eb without feeling funky. I play with 11s on 24" scale, and it feels great in E standard, much like 10s on a 25.5" feel.
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Its a 25.5, So I guess D Standard will do (DGCFAD) I currently have it on Drop D (DADGBE) And it sweet as hell. But it seems I will look for thicker strings..
Thank you for your help.
There are a lot of factors to consider when looking into drop tuning, bigger isn't always better. Some strings offer a large core wire which will help off set the drop in tuning with more tension. However it can really depend on playing style and personal preference.

Also I would recommend getting your guitar properly set up (or doing it yourself) when going to a heavier set. The larger/heavier strings will put more tension on the neck and could cause damage if you're not careful.