i personally say more cubes and more port area... but maybe thats just me. Like 5 cubes after all dis and 80-85 SQ in of port tuned around 35hz.
In my experience imp rise goes up when the box gets smaller meaning you will be getting less power outta your SAZ3500D... If i were you id get a clamp meter and a DMM and see what your amp is putting out now for power from this you will be able to calculate imp rise. Use this if you dont know ohms law, http://www.the12volt.com/ohm/ohmslaw.asp
On my lvl 4 it was wired to 1 ohm but with imp rise my amp was seeing 3ohms, 56.5volts/18.6amps. Thats what i got from my dmm and my clamp meter. This was in 4.3 cubes after all dis, 45's in all corners and 70 SQ in of port.
One thing that has to be factored in here is efficiency and larger enclosures are generally more efficient