All of the seasnoic X series, aside from the 1000W or old 860W, are 160mm, allowing to install the bottom 140mm fan on the R4, i own an R4 + X660 + 140mm bottom fan, yo do need to place them with the fan facing the bottom as the other way around wont fit cause of the location of the modular connectors, i leave you a pic so you get a better idea.
I believe that the Corsair RM are also 160mm, at least the RM450/550/650 (the 750/850/1000 are bigger), by the pictures the modular connectors are in the same disposition of the seasonic, so you will need to install it with the fan facing down.
Only problem with those particular X units is they're overkill and expensive. I have actually been comparing many PSU images together with your image since it's so useful as a reference
. It's actually thanks to you for inspiring me on this 3-intake 1-outake fan setup
Yes, the Corsair RM650's 160mm depth should fit. I wasn't sure whether it's recommended over the others. Also, do you know if the Fractal R4's bottom drive cage can remain in place with a 140mm bottom fan? I wasn't sure since you have yours removed.
I don't know why do you compare the RM with the R3, as FD Newton here in Italy are usually far more expensive.
They have not dissimilar performances, but there are chances the RM would run quieter most of the times: so personally I'd go for it.
The Newton (165mm depth, but should still fit) is also more expensive in Canada (about $30 if I price match other competitors). I just didn't know whether the better quality components and Platinum rating in the Newton is worth buying over the Corsair. Why are chances higher with the RM if both units are semi-passive? i.e. if my peak load won't reach 300W then wouldn't both fans be off?