I ride at both Spring Mt and Green Lane Reservoir during the warmer months. I haven't done it yet but I'm sure you could easily combine the two via the Perkiomen Trail.
I ridden the Perk trail a few times as well but never combined them all in a day. I would think the total miles would be about 25-30. I really have no clue and never will since I don't own a bike compu thingy but anyway.
My plan would start at the Equestrian Camping Area which is the "Blue Trail" trailhead which is off of Hill Rd. Ride down the hill towards the Deep Creek/ Upper Perk side and hit the Perk trail and head towards Spring Mt. Do the loop up/over and back down Spring Mt which has some cool log rolls and other stunts and then take the Perk trail back to Green Lane and do the Orange loop and then head back to the start.
I know both of the trail loops well. Just gauging interest and this is a warm weather type ride. A dry ride too since the orange loop at GL drains like crap...