Depends on what you are doing with it.
I run 28 gatorskin hardshells on my CX (Boardman CX Comp, now upgraded to 105/ultegra level), because they are the smallest tyres I can fit on the rims (according to Sheldon Brown).
Acceleration is effected by the weight of the wheels, which also effects climbing significantly. Bigger tyres = more weight, regardless of rolling resistance and whatnot. Then again, you live in Perth where I suspect you'd call riding over speed bumps "hill repeats"

, so their effect on climbing won't make that much difference. On a wed am training ride I often go on I spend most of my time near or on the front on my roadie. This does not happen on my CX. I certainly end up near the rear on anything with a gradient > ~3% on my CX, when I'd be near the front on my roadie.
However, the advantage with 28s is that you can "just ride over that sh...stuff" and run a lower pressure. So more comfortable. The 28 gatorskin hardshells seem to be significantly longer wearing than the 23mm gatorskins I use on my roadie (and the schwalbe durano pluses I have used as well).
For commuting, not a great deal of measurable difference WRT the time it takes, but it feels like more work with the 28s on my CX vs 23s on my roadie.
Then again, the wheels - without tyres - are probably 0.5 - 0.75 kg heavier on the CX, so it is difficult to say if the tyres do have that much impact.
FWIW and perhaps OT, knobblies wear down very quickly on asphalt.