1800gph is an awful lot. At that point, the limiting factor could be the overflow teeth themselves not being able to handle the flow.
Something to consider with AGA: They use those LAME Mega-Flow overflows. They're the large curved ones with the extremely poor design. The overflow teeth are only on the front, not wrapped all the way around. They have this silly dual-layer overflow setup that's supposed to help pull water from the bottom of the tank, also, but I can't imagine why you'd want that. In addition, the lower half just gets clogged up in time anyway. Also, since they're curved, you can't clean the coralline off of them, which is important to me (though it's not important to everyone).
That said, I have an AGA. I bought it used, the price was right. I ended up cutting off the overflows (what a pain) and putting on my own square DIY overflows so I could keep them clean, and have teeth all the way around the top, rather than just up front.
I've never heard of any problems with Perfecto, but I don't have any real experience with them. Another consideration would be Visio. If you can find a Visio dealer in your area, they are amazingly inexpensive (in line with AGA), are built much better than AGA, and aren't built until you specify how it's built (dimensions, locations of holes, etc.). This allows you to have good size bulkhead holes drilled below, and/or cool add-ons like black silicone, instead of the cruddy clearish-white stuff.