If your question is: "Will I get better performance in OS9 by booting OS9 instead of Classic?"
The answer is absolutely, yes.
Will it still feel slow compared to a Quicksilver also booting OS9?
The answer is also, absolutely, yes. BUT
Nowhere near as much difference as with OSX.
How much difference depends on which model Quicksilver, since there are many with big differences in performance.
The fact is running 10.4 + Classic on a 700 Mhz iMac is pushing the iMac to its absolute limit, beyond what it was designed for.
AND: Running OS9 natively is always better and faster than Classic mode.
Especially if you only have 1MB of RAM…