I'm a fan of using the minimum light possible for long-term 'scapes
With good CO2/ferts, 2 x HO T5 along the length of the tank is normally ample for the vast majority.
I've also had success with 2 x T8 @ just 1wpg.
2007 AGA Aquascaping Contest
I'm going through a bit if a mad 'scaping phase in my 80cm ATM, so high light (4 x HO T5) is used to get fast growth, so I can squeeze out as many layouts as possible in the year. The tank isn't in my main viewing area so I'm happy to see it go through the several ugly pruning transistions before it's finished.
Another aspect worth considering. Compact growth. If you want compact growth, say in HC or downoi, is high light necessary?
Cheers.