I was in a similar situation, I could have got one really cheap from the shop I work in, but after seeing the flow even at it's lowest setting (had to test a customers fx5 in a 4 foot tank), I decided against it and went for a fluval 305 for my 190 litre corner tank.
The loaches would be perfectly fine, the plecs would be OK too, but any fancy goldfish would get completely pummelled and while regular goldfish could probably cope, It wouldn't be fun for them.
If you really want it I guess you could DIY yourself a really long spray bar and put a big sponge over the intake, but really it's such overkill and impractical...it's a big filter, consumes more power, and would be harder to clean out than a 405. After you have taken all those measures, the results would be similar to a 405 anyway. Since the 405 is adequate, you would have the same amount of filter bacteria present as you would with the 405, only in the fx5 there would be lots of surface area on the biological media unused by the bacteria

.
Though if your going to be upgrading your tank to something significantly larger in the future (which you will need to do anyway if you want to keep the fish), the fx5 may be a better choice.