It's a problem that DCF is per BOINC-project and not per application, since there can be large variations in DCF based on which WCG-project you've run before.

But, even if you're running only Rice, and each Rice-wu takes 7 hours +- 1 minute or something, the estimates is still not correct, and this is due to WCG is constantly "adjusting" the estimates... Now this of course makes sence for HCMD2 and so on, there different batches does have variable requirements, and can't always accurately estimate this before starts distributing the work. In Rice on the other hand it makes little sence.

Due to the constant re-adjustments of Rice, I've currently got these various estimated cpu-times on the same computer for unstarted Rice-wu's:
7:00:39
6:46:51
6:53:45

On another computer, the lowest estimate is 6:43:50, meaning if anyone is running with a 10-day-cache with this incorrect estimate they'll have 9.6 hours too much cached work than can be returned by the deadline...

So, even if you're running only Rice, and variations in cpu-time between Rice-wu's is negligible, it's not recommended to use a 10-day cache-size, since some work will be too late. Better would be to use max 9, if you needs to cache lots of Rice-work to reach your badge-target before the end.