i reckon 6x2x27 will look good, the only thing probably is if you have a tall tank, it's harder to clean it without those magnetic thing, or it's just harder for you to reach the bottom if you want to re-arrange stuff.
I was thinking about doing a few drawings on paper first as to how i want the tank to look . Hopefully this will save some time in the rock setup. I'll be taking live rock from my old tank ,there's about 40kgs in it, i'll also be getting 20kgs of rock with the new tank. I'll keep you posted mate, tnx for your input,