You didn't mention what kind of parts you're making, but for a 400mm HMC, it would take one seriously impressive machine, to impress me as much as a new Makino A51NX.
I've watched Makino's webinars on the benefits of their machines, (which are excellent - if you haven't seen them already, watch them ASAP) so I had been wanting to see one in person for quite a while.
The shop I worked for previously purchased one about this time 1 year ago.
First impression - the machine is TINY! As in, they have really reduced the foot-print, which is a good thing.
Second thing to notice - the linear guides/rails are HUGE. Not just big for a 400mm machine - big by any standard. My current employer has (11) Mazak HCN6000-2's, which is a 500mm, 50-taper HMC, and I've seen them many times with the sheetmetal off. Without seeing these machines side by side, I'd easily bet that the Makino A51's linear rails/guides are as big, or bigger than the 500mm Mazak machine's.
Third thing - I have never seen a machine move like this A51... While the A51 is listed as 2,362"/min (60,000mm/min) rapids & 1G acceleration - fairly standard for 400-600mm HMC's - the way that Makino has the servo's tuned is remarkable. I have never seen a machine transition through rapid moves, and into feed moves like this machine. It accelerates/changes directions so fast during high-speed-machining cuts [in solid-aluminum mill parts] that it's a little worrysome really. Crazy acceleration in feed moves that you really can't "see" on paper - you have to watch it cut... In fact, a Brother Speedio may be able to out-accelerate an A51 rapid-point to rapid-point, but I want to see the machine that would out accelerate an A51 during cutting... That would be an impressive machine for sure...
IF we were talking about 50-taper HMC's that were doing true heavy-duty cutting, then I think I'd give the nod to Okuma. Their MA line is seriously impressive for heavy cutting. In fact, I want to see the machine dollar-for-dollar that could out cut one of their MA-series machines, in terms of heavy-duty cutting.
Being as we're talking 40-taper machines though, I think you'd be hard-pressed to out-do an A51. Perhaps maybe something from Enshu if we were talking about automotive die-cast parts. Enshu has 3,543"/min (90,000mm/min) rapid machines, so I'd look into them if they had support in my area. BUT, I wouldn't be on Rapid's alone to out-perform an A51, in-cut. I don't know much about Toyoda, and have always wondered what made them so special to be honest. I know their playground is in automotive machining, and I suspect that is because of their relationship to parent company Jtekt/Toyota's ties to the auto industry...
Edit: I kind of sound like a cool-aid drinking, Makino fan-boy there, but that would be a lie. I'm actually a card-carrying Okuma lover, but am really just a sucker for a well built machine. Credit where it's due, Makino has hit it out of the park with the A51 line...