Are there any more details you can add to this?
LAN access via filemaker client, WAN access via filemaker client, or Web access via browser?
Projected number of simultaneous users?
In addition, how you structure your database and design layouts will have much more impact on system responsiveness than simply the number of records.
If you frequently have to search or sort on unstored fields with large numbers of records, for example, the system will soon slow to a crawl. If you can design your tables and scripts so that such operations are not needed or are very rare, the system can respond pretty quickly even with large data sets.
Can it handle it? Yes. Is it optimal? No. Most likely based on what you have said, I would most likely keep it in SQL.