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A. Yes, some states have restrictions whereas in others when towing a caravan you can travel up to the maximum speed limit as signed. 

Your tow vehicle may also specify speed limits if towing trailers above a certain weight.  Some caravans specify a maximum speed limit. These must not be exceeded. 

Western Australia

Speed is limited to 100 km/h when towing any trailer, or the signed maximum speed limit if less than 100 km/h. 

There are no speed restrictions applying to caravans and trailers other than the signed maximum speed limit.

If the number on the speed limit sign is over 100 and the driver is driving a vehicle with a GVM over 4.5 tonnes or a vehicle and trailer combination with a GCM over 4.5 tonnes, the speed limit applying to the driver for the length of road is 100 kilometres per hour.

There are no speed restrictions applying to caravans and trailers other than the signed maximum speed limit.  The highest speed limit zone in ACT is 100 km/h.

Australia Capital Territory

Sourced from New South Wales Legislation Road Rules

Victoria

There are no speed restrictions applying to caravans and trailers other than the signed maximum speed limit.

There are no speed restrictions applying to caravans and trailers other than the signed maximum speed limit.

There are no speed restrictions applying to caravans and trailers other than the signed maximum speed limit.

There are no speed restrictions applying to caravans and trailers other than the signed maximum speed limit.  This is subject to the vehicle being less than 5 tonne if a bus or 12 tonne for other vehicles, in which case the maximum speed limit is 100 km/h.

A maximum speed limit for towing trailer of 90 km/h appears in some references and publications, but this was removed some years ago. 

Driving on unsealed roads: On the 1st of February 2014, a new maximum speed limit of 80 km/h was applied to all unsealed roads in Tasmania, unless otherwise signposted.

80 km/h in country areas on an unsealed road

100 km/h in country areas on a sealed road.

Most roads in Tasmania have speed limits of 100 km/h or less, with only a few such as the Midlands Highway a limited to 110 km/h. 

# However, if the number on the speed-limit sign is over 100 and the driver is driving a bus with a GVM over 5 tonnes, or another vehicle with a GVM over 12 tonnes, the speed-limit applying to the driver for the length of road is 100 kilometres per hour.

Sourced from Speed Limits on Tasmanian Roads

A speed limit is a maximum, not a target.  When towing, be aware that you may be travelling slower than other traffic, so pull over when safe to do so to allow other traffic to overtake.  Heavy haulage drivers prefer you not to slow down and/or pull off the road as this will slow their momentum.  See the preferred method on Sharing the Road with Trucks.

Travel safely when towing exercising extra caution, and slow down in wet or windy conditions. 

You may also be interested in this question:

Q50 I heard that in South Australia you have to reduce speed to 25 kilometres per hour when ever you see flashing blue and/or red lights of police or emergency vehicles.  Is this on all roads?  Is it only in South Australia?