use asynchronous representatives threadpool.queueuserworkitem large parallelism?

i have .net concentration processes around 300,000 annals collection import, takes few seconds per record i parallelize this. following code, what's inadequacy between processwithansycdelegates() processwiththreadpool()?

public category resultnotification
 { open eventhandler eventuality success;
   open eventhandler eventuality fail;
   middle vacant notify(bool sucess) {if (success) success(); else fail();}
 }

public stationary category processor
 { open resultnotification processwithansycdelegates(record record)
    { var r = new resultnotification();
      func<record,bool> processrecord=new recordprocessor().processrecord;
      processrecord.begininvoke
                     ( record
                      ,ar => result.notify(processrecord.endinvoke(ar))
                      ,null); 
      relapse r;    
    }

   open resultnotification processwiththreadpool(record r)
    { var r  = new resultnotification();
      var rp = new recordprocessor();
      threadpool.queueworkuseritem(_=>result.notify(rp.processrecord(r)));
      relapse r;
    }
 }