i would go with the Emperor line personally, i find that it is a better made product then their penguin line. the 400's are personally my favorite because you can put different filter medias within the it all. Personally it is up to you and what you really want. Your 46 gallon though would benefit from the emperor 400 and maybe even another one if you want. your 75 would benefit from 2 400's but then again ... as i said it is up to you.
Lunchbox ... "i'm a man, but i can change, if i have to, i guess"
Tankless ... for now ... until i find what i really want (and what the wife lets me get!)