Im just gonna go with 1000w hps. Def gonna get both bulbs.
1000w shouldn't be excessive in my 4x4x6 right?
Its 1000w dimmable
Nah 1kw is not too much if you cool it down enough. 600w i would say is more like what you should at least get and 1kw is most you should get.
If you can score two 600w ballasts for a good price, used for example and would not have to pay much more than for 1x 1kw ballast then i recommend 2x 600w instead.
600w HPS has better efficiency than 1kw bulbs ad if you were going to use the 1kw at superlumen setting, it will use 1.1kw, so almost same electricity cost than 2x 600w, but less efficient. Its not like night and day difference in efficiency, but personally i would rather spend 100w more in electricity and get more efficiency. Also if you have 2 separate lights, you can spread the light more evenly, which is always good. You would also ofc need two cooltubes if you need cooltubes in your grow area, so that might ramp up the cost if you want good cooltubes. And remember that good cooltubes also have better efficiency than crappy ones.
Another option would also be 600w HPS + 315w CMH. CMH is quite expensive still, but it has a very good spectrum for resin production, while HPS has good spectrum for bulking up buds. Some swear by this combo, i have not tested, but makes sense in theory and if some say it does work, well it is believable.
1kw is also good, dont get me wrong, but im just saying these because they can get you bit more efficiency if you want to maximise electric cost to bud ratio.
Also you dont ned 1kw MH bulb, 600w is plenty enough to veg, 1kw for vegging would be jsut a waste of electricity cost. And if you were to go with CMH + HPS combo, that 315w CMH is plenty good for vegging also and would cut your vegging electricity bil lto half compared to 600w MH. CMH might not give you better yields, but it will give you better quality and same amounts if you also use the HPS and not CMH only for blooming.