Well that certainly is good news.
392mph max at alt, 343mph max at deck. The figures look about spot on from what I'd expect from a typical Ki-84.
Was expecting something around 350 at deck for an optimistic view of things, but 343 isn't too bad either.
However, it could be a double-edged sword in some occasions. Especially at high alts. Whereas the old Ki84 we had could retain 392mph max speed and optimum climb rate indefinately, now the Ki84 is hampered with limited overboost issues.
Here's an OTD speed list made by whels from version 1.10. AH2 has seen some minor changes, but I think it'd still offer a nifty measurement on just how much more juice the Ki84 got now:
OTD speeds with WEP
----------------------------
TEMPEST 386
LA-7 380
F4U-4 378
190D-9 375
TYPHOON 370
P-51D 367
109G-10 366
TA-152 361
SPIT-14 358
F4U-1 358
P-51B 358
F4U-1D 357
F4U-1C 356
LA-5 356
YAK9-U 355
190A-8 349
190F-8 349
P-38L 344
P-47D-11 344
Ki-84-Ia 343 (new and improved)
P-47D-25 340
P-47D-30 340
109G-2 340
190A-5 339
MOSQ 338
YAK9-T 336
109G-6 336
109F-4 332
C205 331
F6F-5 330
Ki-84-Ia 324 (old and inferior)
N1K2 324
SPIT IX 319
110-G2 316
C202 315
KI-61 313
SEAFIRE 302
SPIT V 302
110-4B 300
FM2 297
P40E 297
109E-4 292
SPIT I 291
A6M5 288
F4F 275 no wep
A6M2 275 NO WEP
P40B 275
HURR IIC 273
HURR IID 265
HURR I 261
Not too bad. Not too bad at all, in fact.
The Ki-84-Ia is now ranked at 20th place in top speed(prop planes). Among the 19 faster planes, four of them are perked which you almost never see in the arena, and three of them are F4U-1 variants, with virtually identical speeds. Two of them are 190As or models essentially based on the Anton(A-8 and F-8) and two are P-51s.
So, if you remove the perked ones and count variants with minor performance differences as one, the Ki-84-Ia's the 12th fastest plane on deck, three planes ranked above it are under 10mph range of difference.
The Yak-9U, La-5FN, F4U-1, Bf109G-10, P-51s, Typhoon, Fw190D-9 and the La-7 will outrun it with ease. Exclude the Hog, the Yak, and the La-5FN out on grounds of rare usage in the MA and basically under typical MA condtions only about the Fw190D-9, Typhoon, P-51 and the La-7, Bf109G-10 will outrun it - the five fastest non-perked planes in the list. Anything other than those five planes, would not be in the 'untouchable' speed difference from the Ki-84-Ia.