On a tank that size you could "get away with" 2 T8 tubes, HOT5 would be nicer, but 4 would be great for high light plants :) T5 tubes are more efficient per watt than T8 and are also a higher wattage, but usualy cost more. Don't bother with low output T5...
If it was mine I would get a double 3 foot HOT5 aquarium fitting with good tubes. Back in Perth I was using arcadia T8 remote balast units with aluminium reflectors with good results, I got some very cheap through work :)
Have a look on ebay or your local aquarium supplier, remember try to get tubes designed for growing plants for better results.
Cheers
George