I've been working with Excel for quite a while for some statistical analysis that I do regularly. The size of the data that I'm working with has gotten much larger as of late, however. The layout of the databases in question is quite simple, usually just three rows which includes a UNIX timestamp, and EST value, a proprietary numeric value and finally an average of the rows that have a timestamp +/- 1000 that row's timestamp (little AVERAGEIFS() formula). That formula and the EST conversion are the only formulas in the sheet.

I'm beginning to work with files with 500,000+ rows. Running the average formula down the entire row takes forever. The end result is the production of print-worthy graphs. I'm looking for either a UNIX CL utility or separate spreadsheet/database application that can handle this amount of data without melting my CPU or making me wait an hour. Is there anything out there?

TL;DR: Simple excel sheet with over half a million rows is getting too slow to work with. OS X alternatives?