I'm going to get a G Loomis Imx rod for a jig rod. Should I get a rod with Heavy stiffness or Extra-Heavy?

What size jigs? I use med/heavy or heavy for 1/4 to 1 oz jigs depending on the actual rod.

 I use med/heavy 853 for 1/4-3/8 oz. and heavy 854 for 3/8-3/4 oz

id get a medium heavy (3 power) loomis rod for most jigs, or a heavy(4 power) for larger jigs and/or heavy cover.

Heavy, extra fast. 

Hootie

Medium Heavy Extra Fast.

you would be better off with the extra heavy 855C JWR ....

In the northeast I think you would be fine with a MH/F. Unless you are fishing in the slop for double digit bass (ie. Alabama, florida etc..) a heavy might be overkill.

the real question is what size jigs is the OP using ? what kind of cover? how deep ?

1/4 oz. jigs can be fished on a medium in some situations as a 5/8 -3/4 jig would need a heavy/extra heavy rod in deep water on a long cast , lots of varibles ...