I used to run Geodes of this type (PCEngines Alix), believe me the oldest Pi wipes the floor with a Geode.
If your service is NTP on a LAN there is no way your Pi will be hit by hundreds of requests/sec.
Besides, set NTP to send time via network broadcasts on the LAN, clients to listen to broadcasts, and you'll get 0 hits/sec.
To me the issue will be elsewhere. Because the Pi has no RTC clock, upon reboot...
- ... The server can change date by a large amount. NTPd doesn't like that, linux doesn't like that. There are conditions where the ntpd server will go poof right at the moment it becomes usable for clients. Personally to keep ntpd in check I use the watchdog program.
- ... The server can change date incrementally, for a long time (days or more). Everybody will have a slightly wrong date, or will be using the backup Internet time sources you've chosen. So much for running a perfectly good stratum-1 source. Personally to avoid this I run htpdate at boot (and watchdog runs it if the server went down) in order to step the clock close enough to the exact date for a fast sync.
I, for one, remember posting a few messages on these issues, look around the forums.
"S'il n'y a pas de solution, c'est qu'il n'y a pas de problème." Les Shadoks, J. Rouxel