It depends of course of the tires!
If you put heavy wide ETRTO406 tires, it won't do the job.
Even on hills, if you mount a lightweight fast wide tire on a ETRTO406, it will be faster than ETRTO451.
A small overall wheel diameter won't change anything, try ETRTO406 with Greenspeed Scorcher 40x406 (the fastest ETRTO406 tire, much lower rolling resistance than any ETRTO451 tire), you will fly on your hills!