A "1000w" dual arc bulb is NOT 1000w worth of light. Its 600w worth of light in one spectrum, with 400w worth of the other. Also, the globes are MUCH more inefficient than single arcs, so the 600w side may only be 400 true watts anyways...
Get a 600w hps, and a 400w mh, and run 2 cooltubes next to each other, under a huge batwing reflector...it will accomplish the same thing, but with much more penetration and energy output.
The reason a MH bulb is advantageous towards the end of the grow, is UVB is produced by MH bulbs...and trichs are produced more abundantly in the presence of UVB. You could accomplish the same thing by getting a UVB lamp from your reptile store...run it on a timer...15 mins on, 45 mins off...thc develops under UV, but is also broken down by it...So we want the plant to know theres uv there so it produces, but not lose too much thc to degradation.
prot