Yikes that doesn't sound good, and I would find it most annoying. I know you mentioned "I sense some other tasks may be slower but not sure." It's important to know: Is Datebk5 the ONLY app that's slow like that? If you have a lot of contacts and the address book loads ok, and/or calendar and Built-In "ToDo/Tasks loads okay I'd say it's an app problem. You said your native datebook loaded okay - if that contained all your database info then it's a Datebk5 thing. It is a HUGE application, after all.
If anything else is slow as well, then I'd say it's your "slower clock speed" TX in general. It (slower clock speed) shouldn't make a difference for "basic" applications, but perhaps it is slower, a la LifeDrive. I'd be interested to know what you find out before I plonk down my $$ for a Tx, which was the plan. I dumped AGendus in favor of Monthly Planner, which I think would load quickly on an etch-a-sketch seing it's only 133k - but if tasks/calendar/contacts are slow as well, then the TX might be a non-starter and you might consider (don't panic) returning it for a refund if it's obviously slower than the Clie you had.
Addendum - had anothr thought - are there settings in DB5 like AGendus for "keeping to-do's in optiomal order?" I know that stuttered the Agendus startup - perhaps DB5 has a setting to "allow" faster opening?