I did quick research on the fixture models to get my numbers. It's not surprising that Serra Ava informs me that these fixtures come in a variety of wattages. It doesn't surprise me, these are some decent fixtures.
I still think you need to ugprade to another dimmer pack. While you're getting 100% draw out of the dimmer pack, you're not delivering 100% to some of your fixtures(probably). If you're drawing more tahn 600-watts/channel, this is definately not the right fixture for you. Not delivering full draw to the fixtures you are talking about using should have little to no impact on bulb life, just diminished performance if it's something that is expected to be drawing more than 600 watts at it's 100% operation. Can't draw more than is available.
I also agree with Serra Ava's advise of moving to the DP-604B. I was a bit unclear about how much current it can handle, it appears to handle 40-amps of current via 2 20-amp circuits. I do not know if this is shared, balanced or distributed between all 6 channels though.
I was personally thinking the RMD series of dimmers might be the best option.
However, seeing as you were leaning towards a relatively compact hanging dimmer, the DP-DMX20L seemed the ideal solution, especially for the price.