Yeah I have both and both are modded in my case. I have lambskin ori pads on my HE-400 and vegans with honeycomb grilles on my M1060.
The he-400 with the ori pads are really, really good, and probably get the most head time out of all of my current headphones. Punchy bass, smooth, forward mids, and crystalline highs without the 10khz mountain they have stock.
The M1060, in contrast, is warmer, with less forward mids and treble. The bass has more slam and body thanks to the larger diaphragm. However, the timbre of the mids are more harsh and metallic, even with the vegans. If you aren't going to mod the M1060, I probably would bother with them. The stock grilles and pads really hurt the performance IMO. However, they are capable with a little modding and the right amp.
But based on everything I have read, an open M1060c is superior to the regular M1060 in every way. So I would say get the C if you are considering a M1060. Anyway, I hope that helps. I can compare specific aspects or songs if you would like. Just let me know.