You mean THEN put a 5000lph powerhead on a 4 foot tank. :thup:
I used to have a Laguna PJ5000 in my 4X2X2 along with a pair of 3000LPH Seios and 2 CF1200s. So that's ideally a total of about 15,000 LPH. It was a reasonable amount of current, but not overwhelming. I've taken out the pond pump since then, so with just the two seios and 2 CF1200s it's pretty calm. But not stagnant looking like most tanks.