The final refinement of the SK lookup table method comes when you add an MD5 checksum column and leave them permanently populated. Use these tables to quickly determine update/insert for only changed or new records. You can even make one of these for the fact table itself. Then fast incremental loads for the entire process become possible and your times will be cut dramatically. I've dealt with source systems that put out flat file dumps of 500+ million rows daily and used this method to process the deltas in barely an hour.