Yes, 48" (54w) T5ho lamps can be overdriven to about 83-85w using Icecap ballasts. The same bulbs will run at 54w with a spec ballast.
Depending on how deep your tank is, you may not need to overdrive the bulbs. IMO a tank less than 24" deep can be lit just fine with normally driven lamps, no need to overdrive them and cut bulb life.
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