The uploads contain some small files and one large file. Several smaller files instead of one big file would not make any difference; the total upload would be the same. Uploads can resume if interrupted.

You might not have a good connection to the GPUGrid server. Depends on geographical location and your ISP. Sometimes ISP's reduce bandwidth at certain times.

Smaller tasks contain less information and each task would therefore upload in a shorter time. Averaged over a week however, the long tasks would probably require less bandwidth. If you want, you can configure your preferences from here,
http://www.gpugrid.net/prefs.php?subset=project

Edit GPUGRID preferences
Run only the selected applications ACEMD standard
ACEMD beta
ACEMD for long runs (8-12 hours on fastest GPU)

You can test your connection (to Barcelona) using SpeedTest and PingTest
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FAQ's

HOW TO:
- Opt out of Beta Tests
- Ask for Help

Unfortunately large result files are important for us as much as sheer computation. They allow us to "see" what happened during the simulation. In general they should be proportional to computation (i.e. long runs have large uploads).