I take it that you're referring to using the Catalyst UI in Linux to access AMDoverdriveCtrl, but I'm not sure what you mean by 'limiting'. Anyways. the frequency-limits are still there in the command-line method (Ubuntu12.10 Linux, perhaps other Linux flavours too where 'fglrx' or 'fglrx-updates' driver are installed) as described below.

Open a Linux terminal
Type aticonfig
Press the Enter key
A help file displays next (within the terminal window)

Hope this helps.
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We'll do it again, any time, any place.

Overclocking the GPU? Then think cooling.. think GPU fan-control FIRST !

Type:
aticonfig --pplib "set fanspeed N xx"

where: (type also the double quotes in the above line)
N = device number
xx = percentage fan speed

to get list of device numbers (in case of multi-GPU setup), type:
aticonfig --list-adapters

to reset everything back to default/non-overclocked values, type:
aticonfig --odrd
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Like a child in each of us, every one was once a noob. No body, but no body, is exempted. Besides, only the wise and learned acknowledges that he/she does not know much about most everything. Come to think of it, that's very much like... me, forever a noob !

With not much overhead, Linux has reasons to be more efficient. It's the GUI that carries a lot of overhead. It's an exercise in compromise: the efficient is not as easy to use, and the convenience of ease-of-use makes for not much efficiency.

P.S.
I wonder why there is no function that does a 'read' of the fan speed, which seems a basic function to me. Maybe the Linux guys know that what is typed is remembered anyway, and therefore one only has to scroll to/from to review what was set. Talk about efficiency or no un-needed extras as much as possible, I take that as a testimony to the Linux efficiency.
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