Suspension Suggestions Needed

[Mustang5L5]

Main differences between the three you list is the top one lacks the sway bar mount, and the two two are the extreme duty arms and the bottom one is heavy duty. Difference there is the bushings. You'll see the HD arms use a poly bushing in one location..ideal for mostly street driven cars. If you are doing a mostly track car, you'll want the extreme duty arms. Difference would be NVH

 

[cleanLX]

reviving this thread. Looking at adjustable MM LCA's. This won't be a track car, but want to gt suspension right. Have subframes from MM already, starting with LCA's, and then looking at shocks/struts/springs or coilovers. Starting my winter project purchses now to spread out cost.

Differences between these three? (other than price?)

$459
https://lmr.com/item/MM-MMRLCA341/maximum-m-adjustable-rear-lower-control-arms-mustang-79-98

$459
https://lmr.com/item/MM-MMRLCA32/79...justable-Extreme-Duty-Rear-Lower-Control-Arms

$379
https://lmr.com/item/MM-MMRLCA2/79-98-Mustang-Maximum-Motorsports-Adjustable-Rear-Lower-Control-Arms

I can see why you are confused.
The description for the 2 adjustable arms is the same, but they clearly are not.
As 5L5 noted, extreme has spherical bushings at both ends (great on the track, more harsh on the street), while the HD has spherical at the axle, poly at the chassis (good compromise, still not a "plush setup, but more enjoyable on the street than all solid).
You noted straight line performance is your biggest concern, so, I'd look at Baseline upper control arm relocation kit, and forego the TQ arm and panhard bar.
RangerJoe and I run the "same" rear arms (version of the MM HD, and Baseline upper kit), neither of us make a boat load of power, we both have full weight street cars, and we both run DOT rear tires (not slicks). In the 60' Joe has been 1.5's and I have been 1.61's spinning. Kevin's (Baseline) stuff works.
Joe has a video of his car leaving on street radials (not DR's)... it's most impressive. Check it out (hope you don't mind Joe).

View: https://www.youtube.com/watch?v=uIpvIxTbCyo