it in theory shouldn't make a difference cos it will just hold the bar higher if they where different lengths between them then maybe, they might be shorter to cure any bottoming out issues on the lower arm if you was to lower it alot.

tbh it does sound like it's your ARB bushes cashing the knock, but the high speed stability could be the tracking, top mounts (if ARB bushes have gone your top mounts could also be shot), or lower arms, even a bad shock will cause this.

i no cos i had to replace all of the above to stop my esco being twitchy and unstable, only to have some cunt rear end me a week later and write my car off