Are you putting these in a tent? Running a 1000w gavita DEHPS in a tent is not realistic at all, you need a lot of vertical height. The sunsystem AC/DE hoods are more suited for running dehps in a tent.
Id look into the HLG 600 kit instead of the HLG 550. The hlg 600 kit is $723 prebuilt, and is 620w versus the HLG 550 which is only 510w.
The HLG 550 is closer to a replacement for a single ended 1000w hps, but will definitely give a gavita a run for it's money. The HLG 600 kit will definitely replace a 1000w gavita.
The LEDs will save you a ton on your electricity bill, they'll put out WAAAAAAY less heat, you'll run less risk of light bleaching your plants, you'll actually be able to see your plants under them, and in my opinion will increase quality across the board. Oh, and you'll very likely see higher yields too.
edit: forgot to mention: You can actually veg under the HLG light, whereas you'd be silly to veg under a dehps lamp.