3x 71.99 is still a better price than an FX5... but an FX5 is a hell of a filter. If it was me, Id hang 3 AC110's off the back. Will look better than a hulking canister sitting next to the tank. The FX5 would *probably* be OK. I think they recommend it be 7" below water level, and a 125 is 24" tall, so with your 6" stand it ought to be fine.
Also I may get flamed for this... but for all who are using an XP3 for reference - I have both an FX5 and an XP3 and you can't compare them. I made the mistake of owning the FX5 before buying my xp3, and I hate the xp3. It won't self prime, and it has that hokey valve-locking mechanism on top, and if you get any air in it at all it takes forever to come out, blah blah blah. If it wouldn't have been ridiculous overkill I'd have taken the XP3 off my 50gal, taken it back and bought another FX5.