Some friends of mine from facepunch have made some really well optimized maps, however, they may be a little too small. (I personally recommend no more than 64 players per server.)
RP_Locality Very small download, it won't have room for many cars, if any at all.
RP_EastCoast_v4b Small download, he updates the map every 6 months or so, this map has more space for cars, but the map is still small.
Lowering the max player count from 90 to 64 will significantly improve server and client performance. Please consider this!