I'd use both... The L30 isn't going to be able to keep up with all that restriction assuming you're using a WW/RBX/TDX/6002/6000 WB... Even 3 low restriction blocks would be pushing it IMO.
BTW, my MCP600 may push half the water L30 pushed at zero restriction, but in a single block (WW) loop, it sure pushes a heck of a lot more water than my l30 ever did... The L20's flowrate compares to the MCP600, and since the MCP600 works well in a restrictive setup, I feel the L20 will only add to performance levels, NOT subtract.