Might I suggest introducing new maps to the 2nd COD4 server before you touch your main one.
You guys run a great server stuffed with the most popular maps which is highly ranked and almost always 20/20 slots...
Showdown, Shipment, Pipeline, Overgrown, Killhouse, Farm, Creek, Bloc, Crash (winter) and Countdown only have half the popularity of the ones on your server.
Convoy, CityStreets & Bog are a little more popular than the above list.
I like all maps, so have no great input or requests..
Just be cautious as you already have a great setup..