Both possible as day hikes, A fairly hard-core bushwhacker might do both in a single day. Standard Iroquois is from the Algonquin - Boundary Col. How you get there is harder. From Loj, which is where most come from, requires a trip thru Avalanche Pass & then up one of the steeper trails in the area. Trail climbs 2100 - 2300 or so feet in 1.7 miles. (I may be slightly off as I read this a couple of weeks ago before I descended this trail, it's one of the longer steepest trail sections in the ADK's. ) Other Loj option is to climb over Algonquin first then descend to the Algonquin - Boundary & take the herdpath. Having descended from the to Lake Colden & previously back over Algonquin, I think going back over Algonquin may be easier.
Have not been to Marshall yet but I've heard good things.