Robert,

I use a Beseler 57 enlarger with Aristo V54 cold light head, generally at f/8, for my 5x7 negatives, or an LPL with color head for my medium format and (rarely) 35mm negatives. I need to use longer exposures, about a factor of two, for the color head compared to the cold light head, for an equivalent enlargement. Your 90 sec at f/5.6 for a 2x enlargement sounds comparable to what I need. The longer exposures are for larger enlargements and/or more dense original negatives.

Mark