The difference in light will be considerable. It would take, roughly, five 125-watt CFLs (actual wattage - and NOT the home lighting type and instead real CFL grow light bulbs) just to equal a 400-watt light, so again the difference in lighting would be considerable.
What the person might have meant was for your purposes the CFL would do what you ask of it. Frankly 1000-watts for clones is a tad bit more than would be needed unless someone's light was WAY, WAY away from the clones. For vegging unless you veg to a somewhat short height there is no way in the world that any CFL of any wattage will perform with a 1000-watt light with a MH bulb. Still for the difference in operational costs the CFLs might still give you enough.
You have to decide if you would rather drop all the way down to CFLs or just switch to a lower wattage HID light for clones and vegging or possibly consider LEDs, but IF you do DO NOT consider them unless you can afford to purchase high-quality LEDs and to purchase them in adequate sizes and numbers because if you purchase low-quality LEDs or do not purchase enough of them you will end up wishing you went CFL or stuck to your 1000-watter.