Boot partition size is the issue, not hard drive size. In my case the boot partition is the Workbench partition. I am still using the 46GB hard drive, no problems except I still have terribly slow spin up times.
As a matter of fact it spins up so slow I get the WB requestor and have to 3 finger sulute once. I am not jumpered to have a delay, it's just normal for this half-height drive I suppose:-/ Oh and this drive is loud as hell! :-x