I do a lot of lighting design work for comercial projects....
10' is not that high, mine is also 10' and i have only 4, 2 tube (40w ho) fixtures, in a 25'x25' garage, i would reccomend 6 fixtures for that size (when i redo my garage i will do 6). and you can even run 32 w t8's and have really good output, - if you want better color rending you have to buy a more expensive bulb, (35k temp) i would do all of them, not just a few otherwise it will look a bit funny at source... in a gargage you should get a good 5 years or so out of your bulbs, so its not too expensive in the long run.
metal halide will be tough at 10'.. the correct fixtures are expensive and you will get hot spots unless you buy a fixture with the correct reflector and/or lens. although nothing beats the light quality. if you are doing a living room style garage i would say suck it up and do the MH, (you can pm me and i will help you with the selection and design for your situation) but if its just a regular garage i would just go with 4' flour. and if you want better color, buy warmer bulbs. (gets rid of the green flour. look) - also MH takes about 5 mins to "come on" unless you get a pulse start or re-strike. (don't confuse MH with Halogen)
lastly, lumens at work surface are as much a function of cavity reflectance (light shiny paint on the walls and ceiling) as fixture output. go with a nice satin white on the walls and ceiling, and a ligter colored floor and your garage will light up.
with light fixtures, you pretty much get what you pay for... so think about what you want not just in the way the fixture looks cosmetically, but what kind of use you want and final result you need for lighting
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