I have about 50.000 of records to import in a Magento store. What I have already tested: The file is about 50 MB.
If you disable the indexer while your load runs and then re-enable and run afterwards, it should improve your load time.
$indexer = Mage::getSingleton('index/indexer');
$indexer->lockIndexer();
// ... run your processing ...
$indexer->unlockIndexer();
// Reindex everything
$processes = $indexer->getProcessesCollection();
foreach ($processes as $process)
{
// echo 'Processing: ' . $process->getIndexerCode() . "n";
$process->reindexEverything();
}