I'm big on flow in general. My RFUGs above 10 gallons all use 1140s,at least one per 1 1/2-2 square feet. My current 29 has 2 1140s, but I am going to try cutting it to just one, there are heating issues involved here and I want the tank a bit cooler (there are also two internals in the tank for extra mechanical filt.). My 30XH , which was my first planted RFUG, does fine on a single 1140 and has for multiple years now. If the 29 worries me at just one 1140, I'll try it with one of each, so this setup is still experimental and still subject to revision. The plants and fish (dwaf puffers) are fine in the current setup and those fish can handle the temp fine, but again personal comfort for me - I don't want to have to operate the tank just above 80F.
I prefer the 1140 to the 660 just for the increased flow. Because I use significant gravel beds these days for planting, I don't have confidence in the smaller pump's ability to move water against that resistance. There is also the fact that the 660 requires the adapter in the RFUG tube, and there can be some fine debris bypass in that configuration - which is likely trivial, but I like it better with the tight fit of the 1140.
