According to the elevation selection on MapMyRide for the IMLP bike course it has a total of 4820' of ascent and 4777' of descent. The minimum elevation is 633' and the maximum is 2218'. I don't know how accurate that data is, but it sure makes for some purty graphs with different colors representing the grades. You could map out your ride and then compare the elevation graphs.
The general consensus is that LP has roughly 6000-7000ft of total climbing. So if you REALLY have 4000ft of climbing in 46 miles, that should probably be tougher than a loop of LP.