flash sync speed
Canon 300D / Digital Rebel flash sync speed is 1/200
Canon 10D flash sync speed is also 1/200
The sync speed is one thing, flash duration is another. The more power a flash uses, the longer the flash duration, the less power a flash uses the shorter the flash duration. However, for practicaal purposes, on these cameras, the flash duration is much shorter the flash sync speed, so this is a non issue. Any movement should be frozen, unless you are photographing bullets.
There are also hacks available that make some of the features disabled on the Digital Rebel available (disabled so as not to take away sales from the 10D).
The Canon EF 100 macro is outstanding, and is one of the sharpest lense in the lineup. It is not that hard to make a sharp macro lens, and they definitely nailed this one.
I use both the 10D and the EF 100 macro.