What HP = Extreme Duty?

i would go with the heavy duty with no more mods then you have

ok well i personaly wouldt get the hds i have a 11.5.1 347 with hci on it witha 175 shot of nos and 373 gear and run normal upr componets i dont think you will need the ed

Right from the MM Website:

"MM offers two different types of rear lower control arms: Heavy-Duty and Extreme-Duty. The difference between the two is the bushing configuration. The Heavy-Duty arms are suitable for cars with moderate horsepower levels that are not drag raced. We recommend the Extreme-Duty control arms for any car that is drag raced, and any car with the higher horsepower levels that come with superchargers, larger displacement engines, etc.

To adjust, or not to adjust...
Both our Heavy-Duty control arms and our Extreme-Duty arms are available in two basic styles: Non-adjustable, or adjustable for ride height. These two styles are available with several different options for spring perches and swaybar mounts. This ensures that we have exactly what you need for your car.

Non-adjustable Control Arms
Non-adjustable arms are available with a fixed-position spring perch that maintains the same ride height as a stock control arm, or without any spring perch at all, for coil-over applications. These control arms are available with mounts for a factory-style rear swaybar, or without any swaybar mounts, for use with MM's Adjustable Rear Swaybar.

Adjustable Control Arms
The easy adjustment of MM's Adjustable Control Arms allows raising the rear ride height by up to 2 inches, or lowering it as much as 1 inch. A heavy-duty weight-jack bolt, similar to those used in NASCAR, makes this possible. The spring perch design allows easy ride height changes, with the car still on the ground. Road racers and autocrossers can set not only the ride height, but also corner weights, for optimum handling. A car can be fully loaded up with gear for a road trip, and then have the rear ride height adjusted back up to normal, to avoid bottoming out. These control arms are available with mounts for a factory-style rear swaybar, or without any swaybar mounts, for use with MM's Adjustable Rear Swaybar."

I would say you probably don't need the Extreme Duty now, but you will probably add more power and its better to have the suspension ready now. Besides, you wouldn't want to have to buy controls arms again if you decided to add more power. As for the tires, what size wheels are you using? What sizes are you looking at?

I've got 255/50 on my 16 pony's right now. I'm gonna go to 17's with my 5 lug conversion. From what I've read 245/45's are safe for the front. I'm not sure what I'm gonna put on the rears though.

I think you'll be fine with the non-adjustable LCA's. Unless your doing alot of drag racing and putting really tall tires on the back.

I'm running 275/40 on the back with 17x9 wheels w/ no promblems. I probably could have fitted 315/35. 1.5" lowering springs also.

The upper control arm change was the best suspension mod I did so far. My stock bushings were really bad.

I put on the extreme duty arms this summer, as well H&R sport springs, Tokico adjustable shocks and struts, and the Ford Racing UCA's. My car goes to the track about 3 times a year, and I don't have anything other than a street tire on pony's right now. I like the adjustability, it allows me to get the perfect ride height . However, if I had to do it over again i probably would've used the same design from a different manufacturer for 200 or cheaper. Granatelli advertises the same design in jegs for a good deal less. So if I were you I would check out that option.