I got searching around online to see if I could find any help with this and came across a couple things.

I’ve never seen a strat with a raised trem unit, that isn’t to say that I’ve never seen one at all but according to this link its not all that uncommon.
http://members.tripod.com/~AFH/Tips.html

I’d argue this simply because I’ve never been into a shop and seen a strat with a trem that was like this
http://img111.imageshack.us/my.php?image=strattremhighzs0.jpg

Thats always seemed like a result of high tension which could explain the broken E string. How many springs are in the back cavity of your guitar? if its 2 or 3 then your fine with 9s or 10s if there are more springs then its possible you can move up to a higher gauge of string.

If the guitar only has 2-3 springs in the back cavity for the trem unit then I’d suggest taking a good look at the nut and saddle for that string to make sure there aren’t any little edges or burrs that might be breaking the string if you don’t see any try shaving down pencil lead or getting some graphite dust and just lightly putting some on both the grove for the nut where the string rests as well as on the saddle, try playing like this and see if the string still breaks, if it does consult a tech. I’d consult a tech anyway about the high trem unit. I really don’t think it should be raised.

As for getting a heavy metal sound check out the hot rail pickups from seymour duncan.
http://www.seymourduncan.com/products/electric/stratocaster/cutting-edge/hot_rails_for_s/

I’d suggest those if your guitar body isn’t routed under the pick guard for a humbucker and back to your “which string for heavy metal/rock”
Thats going to depend on how heavy the metal is. If your looking at stuff like In Flames and children of bodom then you may not like the following, You’ll need really low gauge strings as well as a trip to a tech to set you guitar up for incredibly low tunings. In Flames tunes 2 steps down to C the result is C-F-Bb-Eb-G-C. This would require more springs being added to the back cavity on your strat to compensate for the low string tension and the truss rod for the neck would have to be adjusted as well, saddles repositioned, intonation set, ect.

Hope that helps some.

HI, I use 10-48 gauge D’Addario strings, dont suffer with much string breakage, i play Rock covers and heavier rock too, if your strings are breaking on the bridge then get some fine emery paper or wet and dry, and rub down the saddle, it may be a small casting defect on the saddle, or you sould try replacing the saddles with graphite ones, not an expensive upgrade but it could solve your problem.
The worst thing about string breakages is the hassle when you are playing live, i have a SG standard with a Maestro trem and when my string breaks it knocks the whole guitar out of tune, makes it uplayable, and it always seems to happen in the middle of a solo, i have to carry a spare guitar in case of string breakages, setup and ready to go.