best slam from 12" sealed, 1000watts, 1 cube ?
 

suggestions?

my short list thus far is IDMAX and JBL Gti, i'd like to retain some sq but spl is the priority

Either or, you don't get much better than those. I'd pick the GTI. If you had 2000w I'd recommend a SSA XCON (1750w rms). The SSA Icon is also a good choice but many say it lacks output. If you want more output go with two ported 8's in 1 cf3 + port or a ported 10 in 1-1.5 cf3.

You should model them:

Sealed Subwoofer Speaker BOX DESIGN - Qtc Calculator

Fi Q has exceptional output and and does well with 1000rms and 1.cu.ft sealed

well if spl is more important and assuming you are space limited... you should look into a ported 10". In virtually all cases a ported 10" of the same model will be louder than a 12" in a sealed box...plus it'll sound great as well. Here's a simulation using a Jbl w10gti in a ported 1 cube box @ 36hz vs. a w12gti in a sealed 1 cube box both getting 1000 watts. This correlates with my personal experience as well in most mid sized vehicles.

thanks for the sim

the main reason for sealed is the enclosure will be all fiberglass, imo, ported adds too much complexity to that type of build

if I was going ported, I'd likely go digital designs

If ported, use an aeroport sticking out of the box and if you're mounting the box to the side, run the port along the bottom rear of the trunk. Barely noticeable.