from my point of view, acura's top-line model RL overlaps with the G37X in terms of specifications but competes with the M45 in terms of price. in fact, the G37 makes more hp than the RL, yet the G is infiniti's entry model. yes, i know that the G25 recently came out to move the brand down-market a bit, but overall, infiniti's line-up starts where acura's line-up ends.
on the other hand, neither acura nor infiniti have anything remotely close to competing with the lexus LS. Infiniti did at one time with the now-discontinued Q, but no longer. the legend/RL, as nice as it is/was, has never been a contender.
imho, acura<infiniti<lexus<audi<bmw/mercedes. feel free to disagree.