Digital ballasts will save you some power definitely and will not get hot as opposed to a standard ballast. The Lumatek seems to be a better choice since they say that the light efficiency rate of a 600w Lumatek is 50.6. You may also want to look at Galaxy because I think it offers more light output compared to Lumatek. Here is a table that I found in one of my readings:

600w Lumatek (120v)

Watts: 610w - 620w

Amps: 5.1A - 5.15A

Light Output: 12.26

Efficiency: 50.6 (Watts/Light output)*

Time until full luminance: 2 minutes

Bulb: 600w HPS Hortilux @ 29"

600w Galaxy (120v)

Watts: 590w - 600w

Amps: 4.95A - 5A

Light Output: 9.71

Efficiency: 60.7 (Watts/Light output)*

Time until full luminance: 2 minutes

Bulb: 600w HPS Hortilux @ 29" (stopped firing bulb after 2 min on first attempt)

1000w Evolution (120v)

Watts: 1010w first 2 min - 850w after 4 min

Amps: 7.8A - 8.2A

Light Output: Peeks at 16.7 (2 min) then drops to 14.7 (4 min)

Efficiency: 57.8 (Watts/Light output)*

Time until full luminance: 2 - 4 minutes

Bulb: 1000w HPS Super @ 29"

Notes: Fan is louder than the humming of the SSX ballast!

1000w Sun System 6 (120v)

Watts: 1080w - 1100w

Amps: 9.6A

Light Output: 18.6

Efficiency: 59.1 (Watts/Light output)*

Time until full luminance: 6 minutes

Bulb: 1000w HPS Super @ 29"

This video may also help...

Here is a link that might be useful: DIGITAL BALLASTS VS MAGNETIC BALLASTS, HYDROPONICS SECRETS 48

I think versatillity is a key consideration. You may do better buying a switchable ballast. Switchable ballasts allow you to change form a Metal Hallide bulbs to High Pressure Sodium bulb by changing a switch on the ballast, This may be much better for the flowering phase.

I use transformer type ballasts and don't know if digitals are better or worse. I have a friend who says the digitals have ugly wave forms and are hard on bulbs. I have never seen any tests on this.

There are new bulbs that offer MH and HPS both burning at once in 1 bulb. I have ordered one of these to try. The spectrum may be ideal for flowering plants in both grow and flowering stage.

Nelson