What is detrimental to AC motors is high current.
Very few mini-splits use AC motors. Even the low-cost DIY units are
all using inverter-modulated DC motors for the compressors, and usually for the blowers as well.
North America and Japan are 120v.
Actually Japanese grid is nominally 100V /60Hz (sometimes dropping into the 90VAC range) in the southern/western prefectures, and 100V/50Hz the northern/eastern part, with some prefectures that have a mix of both. 200V-250V is sometimes available in some areas, but the residential wall plugs are the same independent of voltage or frequency, making it too easy to plug stuff designed for 100V/60Hz into 200V/50Hz sockets (and conversely). The voltage and frequency divide makes it far more difficult to deal with power imbalances between one end of the country, since there is only a very limited capacity in the asynchronous converters tying one side to the other.
Pioneer told me that the units are able to size down for the appropriate space. Seeing as this is an attic and I don't have room to do r 38, just r 30 in the sloped ceilings the extra cooling power might be useful.
There is no real correlation between floor space and cooling load. An R30 cathedralized ceiling doesn't significantly increase the cooling load relative to an R38 roof of the same size- the window solar gains are a much bigger driver. (Even the color of the shingles makes a bigger difference on peak cooling load than R38 vs. R30.)
It's just stupid to install a modulating system that is so oversized that it usually just cycles on/off at the minimum modulated output, but that sometimes happens when following brain-dead "square feet per ton" rules of thumb. Some one-tonners can't throttle back to under 5000 BTU/hr, which may very well be the design condition cooling load of that space.
Almost all of the newer Pioneer mini-splits are now re-labeled Midea units (which is a good thing- some of their older stuff was pretty junky by comparison). But when comparing apples to apples, keep a sharp eye on the MINIMUM cooling output. Some 3/4 tonners can't throttle down as low as some other 1-tonners.
[edited to add] Curiously, the 1-ton
Pioneer throttles back to 3700 BTU/hr making it more appropriately sized for that tiny space than the 3/4 tonner, which won't back off to less than 5800 BTU/hr, which is probably close to or more than the design cooling load. This is true of both the 115V and 230V versions. Their 3/4 ton units have slightly less than a 2:1 turn down ratio between min & max cooling output compared to a 3.5 : 1 turn down for the 1 ton. This is not typical. [end edit]
The difference in how fast it cools the space is a function of it's maximum cooling BTU rate not it's AHRI "rated" BTU/hr, which is the modulation level at which it's SEER efficiency is tested. They are sometimes the same, but often not. There are many 3/4 ton mini-splits tested at 9000 BTU/hr for it's "rated" output that will deliver 12,000 BTU/hr at max speed under AHRI test conditions, and others that don't. But in either case, you probably won't detect much time difference between a 3/4 ton and a 1 ton, the way you
would notice a cool-down time difference between a 1 ton and 2 ton.