actually you are not overdriving the bulbs, both bulbs are NO bulbs and there for the ballast is supplying the same current level. the only differences is the 32 watt bulb uses less watts. Some time the T8's require a different starting type then the T12's but looks like yours are starting no problem so the bulbs and ballast will last with no detrimental effects whats so ever.
here is a post I wrote to help explain florescent lighting... I wish it would be a sticky so more people would see it.
http://www.canreef.com/phpBB2/viewtopic.php?t=7740
Steve
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