I have a 7 foot high 4 foot x 4 foot base dimension cage and had lots of trouble heating it- it is used for frill necks. To get it to temp over winter i had two ceramic heat emmitters and two merc vapor spotties as well as two 100 watt reflectors- i the night time i ended up heating the room with a fan heater. I have been recomended the radiant heat emmitters from the herp shop for use as the main heat source and just use the spotties and ceramics to top it up.(it will also stop my room looking like the mcg at night or a hydro lab)
I copied the following off the herp trader- perhaps they can advise whith is the best to use for your cage set up.
RADIANT ENCLOSURE HEATERS 
Look great
Blend in well to the ceiling of most enclosures
Pre wired so no sparky required
Available in a range of wattages
No light covers required
These are Radiant Panel heaters that can heat up larger areas for reptiles, birds or animals. The front surface of these heaters are moderately hot so they should be fixed on ceilings where animals or birds etc. will not come into contact with the front surface.
50 watt, 270mm x 250mm - THD050
$110.00 each
160 watt, 540mm x 380mm - THD160
$190.00 each
240 watt, 800mm x 380mm - THD240
$240.00 each
320 watt, 1080mm x 380mm - THD320
$270.00 each
750 watt, 1150mm x 590mm - THD750s
$450.00 each
