Ask HN: Free/Open source software to plot an extremely long dataseries

I've got a 4 column {Time, var-1, var-2, var3}, 6000 row CSV file whose data I'd like to plot as a smooth line graph (3 separate lines). Excel, Numbers, Plot (for Mac) and Grapher, not to mention Google spreadsheet, have all crashed or been rendered unusably slow by that amount of data. Do any of you know of a utility which can handle that amount of data relatively smoothly?