NodeJs performance problem

I'm building a realtime stats application using NodeJs. For the prototype I'm using a Quad-Core AMD Opteron in a RackSpace server for the test with a nodejs server using the Cluster NodeJs ( http://learnboost.github.com/cluster/ ) and the MongoDb using the native nodejs driver.

Basically I've inserted a JS code in my company project that delivers content for a bunch of client's websites. This code "pings" my server each 10seconds calling for a image and passing parameters that I get in the server-side and insert ( or update ) in a MongoDb collection. In a "slow" time of the day I get about 3000 connections ( I get these using the netstat -natp command on terminal) each time that makes my cluster use about 25% of each core ( I get these using the "top" command ). But in a "busy" hour I get about 7000+ connections each time what makes my cluster go crazy ( about 80%+ use of each core ), and it seems that as the time goes by, the node degrades. Is this normal? Or should Nodejs handle these hits in a more "easy" way? If I use Mongoose, the performance can increase?

In case you are curious about the MongoDb it uses about 4% of one core, which is fine by me ( without putting a index the use was about 50%+ but, at least, the index solved this performance problem ).

Thanks a lot for the patience, Cheers.

Edit:

The code that makes the insert looks like this: db.open (function (err, db) {});

return connect.router(function(app){
    app.get("/pingserver/:clientid/:event/:cachecontrol", function(req, res, next){
    event:'+req.params.event + ', cachecontrol:' + req.params.cachecontrol);
        var timestamp = new Date(); 
          switch(req.params.event) {
          case 'load':
              var params = url.parse(req.url, true).query;

              db.collection('clientsessions', function(err, collection)         {
                try {

                    var client = {
                        id: req.params.clientid,
                        state: req.params.event + 'ed',
                        loadTime: timestamp.getTime(),
                        lastEvent: req.params.event,
                        lastEventTime: timestamp.getTime(),
                        lastEventDate: timestamp.toString(),
                        events: [{
                            event: req.params.event,
                            timestamp: timestamp.getTime(),
                            date: timestamp.toString()
                        }],
                        media: {
                            id: params.media.split('|')[0] || null,
                            title: unescape(params.media.split('|')[1]) || null
                        },
                        project: {
                            id: params.project.split('|')[0] || null,
                            name: unescape(params.project.split('|')[1]) || null
                        },
                        origin: req.headers['referer'] || req.headers['referrer'] || '',
                        userAgent: req.headers['user-agent'] || null,
                        userIp: req.socket && (req.socket.remoteAddress || (req.socket.socket && req.socket.socket.remoteAddress)),
                        returningUser: false
                    };
                }catch(e) {console.log(e);}       
                 collection.insert(client, function(err, doc) {
                 });
              });
              break;

          case 'ping':
              db.collection('clientsessions', function(err, collection) {
                  collection.update({id: req.params.clientid}, { 
                                                     $set : { lastEvent: req.params.event 
                                                             ,lastEventTime: timestamp.getTime(),lastEventDate: timestamp.toString()}
                                                   }, {}, function(err, doc) {});
              });
              break;

          default:
              db.collection('clientsessions', function(err, collection) {
                  collection.update({id: req.params.clientid}, { 
                                                     $set : {state: req.params.event+'ed'
                                                            , lastEvent: req.params.event 
                                                            , lastEventTime: timestamp.getTime()}
                                                   , $push : { events : { event: req.params.event, timestamp: timestamp.getTime(), date: timestamp.toString() } } }, {}, function(err, doc) {});
              });

              break;
          }

          if (!transparent) {
              console.log('!transparent');
              transparent = fs.readFileSync(__dirname + '/../../public/images/transparent.gif', 'binary');
          }
          res.setHeader('Content-Type', 'image/gif');
          res.setHeader('Content-Length', transparent.length);

          res.end(transparent, 'binary');
      });
});