Summary or not summary...?

In two database of my solution I need to have summary of founded
records, but never I've interess to have summary of all records, so I
can't decide if I should use summary fields or empty global fields with
a script that calculates summary only on demand. The two database have
now 900 and 23000 records an incrementing 250 and 6000 records/year, and
summary I need are mostly from 20-30 record(sometimes 250) for the first
file and 100-150 for the second; summary fields are 7 on first file and
for in the second and I need only global summary. Will summary fields
slow down my solution or can I use them without any problem?
Adriano B.
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