Thinking about swapping subs

[Lucky4Designs]

I'm thinking about swapping out my Memphis' for a couple of the SA-8v.2's. I love my Memphis', they're pretty loud for the amount of power they take and people can hear me coming from a couple blocks away but design after design, I can't come up with a good box. In order to get the proper 3 ft^3 @ 32hz, I would have to take out my rear seats. Since the SA-8's don't need a huge box for a pair, I was thinking about switching over to them.

Now, if I make a box around 1.8 ft^3 @ 33hz (or any other good box design for a pair), and run 700w RMS to the pair, how much of a difference am I looking at? I know they would be underpowered a bit, but I am in the process of saving up for an AudioQue AQ 1200D and the Big Three upgrade until I can afford my Mechman alt. and a second battery & isolator (would also need battery recommendations). I plan on buying the dual 2-ohm SA's and wiring to a 1-ohm load on the AQ. What kind of a difference would I be looking at here? My Memphis' flex everything. Stuff in my seats flop around, vision blurs a little bit, head unit jumps around in my dash a little bit as well as cans in my cupholders, windshield flex's a little, mirrors are useless, ext. cab windows look like they're ready to pop out, and they broke the plastic trim on my headliner today. I'm just trying to get the most impressive sound with a small system, but I don't want to lose the loudness I already have! Lol yay? Nay?