I managed to move my 240l tank and cabinet without completely stripping it down. It was actually my husband and my Dad that moved it, while I watched in terror. I had to get the water level down to about 10cm depth, and removed the large chunk of bogwood and a small amount of gravel substrate. This was just enough to enable the cabinet to be lifted an inch or so and slowly moved (turned to sit against a perpendicular wall). A lot of care was taken to not tip the cabinet or move the tank in relation to the cabinet in anyway. As I have a drilled tank, the pipes go through the cabinet, and I was very worried about them being damaged. We managed the move with no visible movement between the tank and cabinet.
I did this in May and have noticed no adverse affects. If fact, my tank seemed to have benefit from the 70% water change and the reduction in direct sunlight in the new location.
So I would say it is possible to move your tank sucessfullywithout completely emptying it, but I certainly wouldn't like to do it again. The fish seemed completely unphased, but I was incredibly stressed out by the whole thing!
If your tank has been in that position since October, it may be ok. In which case, I'd echo Chucklett's question, does your tank really need moving? Personally I wouldn't be happy with that sort of level, but will accept that my experiences may have made me a bit paranoid. I'm afraid that I have no scientific evidence to back up any of my comments.
I think you also need to decide whether the level will bug you now that you've noticed it. I can't remember if you've already cycled and stocked your tank, but if not, you don't want to fill it with fish and then wish you'd moved it! It'll be a lot less stressful to do without fish.
If you do decide to move it, make sure you use the spirit level when it is in its final position - before you refill the tank!