What are you on about, "not massive"? they are on the radio constantly and in a pretty high position in the charts. Also they play loads of festivals like glasto and reading as you pointed out.
You're not getting that many posts because it is going fine, if you start to fail posts telling you so will come flooding in; not many posts can be a good thing :)
The amout of lumens will vary depending on the light but with 2 400watters you'll have atleast around 90 thousand lumens ( I think) and with a 4x4 space that is 5625 lumens per square foot, which is an acceptable amount for growing :)
Another question for all of you, I'm only going to buy one light so should I go for the Slyvania grolux (both light spectrums) or the Son T Plus (HPS)? http://www.basementlighting.com/Merchant2/merchant.mv?page=1/PROD/GL400