Оптимизация для string.Join

namespace Allowerd_Server.Object
{
    public class BaseChanelChat
    {
         public List<NetConnection> ListClients { get; private set; } = new List<NetConnection>();
 
         public void JoinClient(BaseClient client)
        {
            if (client.IsOnline)
            {
                client.Chanel?.LeaveClient(client);
                SendPacket(new Dictionary<string, object>() { { "method", "Chanel.JoinClient" }, { "login", client.Login } });
                ListClients.Add(client.Connection);
 
                string logins = string.Empty;
                for (int i = 0; i < ListClients.Count; ++i)
                    logins += ";" + BaseClient.Find(ListClients[i]).Login;
                client.SendPacket(new Dictionary<string, object>() { { "method", "Chanel.SyncClients" }, { "logins", logins } });
            }
        }
    }
}

logins=String.Join(";", ListClient(client=>BaseClient.Find(client).Login));

logins=String.Join(";", ListClient.Select(client=>BaseClient.Find(client).Login));

StringBuilder.AppendFormat();