That seems more appropriate to a -I than a -II, no? I thought there were improvements to the Ki-43's strength in the -II.
The -I was so weak that even superficial damage put the airframe out of commission for a long time while it was repaired. The skin was made thicker so diving speed was improved, but improved as compared to the -I, not necessarily "on par with US planes" if you see my point.
I'm not exactly sure what the VNE speed on the Ki-43-II was, but it was quite easily out-dived by every US plane it ever met. They ripped wings off when dive bombing in -I models, and that was most likely at much slower speeds. I rather suspect that 425mph may be far too generous.
From Saburo Sakai:
The A6M2 had a top speed of 309 mph. and a maximum allowable dive speed of 350 mph. It became extremely heavy
on the controls above 275 mph, and approaching 350 mph, the Zero's controls were so heavy it was impossible to roll. A further comment by Sakai was that the skin on the wings started to wrinkle, causing the pilot great concern, since a number of Zero's had shed their wings in a dive.
If the A6M2, with (by most accounts) better durability than the Ki-43, could only dive 350mph, I doubt the Ki-43-II could go to 425mph. The P-40Bs were limited to 480mph, though some pilots pushed that to 510mph. <-- using a quick google reference on the P-40B.
If anything, HTC should probably bring that dive speed down for the Ki-43. And it should suffer very strong locking on the controls well before falling apart.
Fish: Some field mods stuck a 20mm in the nose gunner's position but the main standard modification was the one in the ventral gondola. This allowed the bombers to also use it for ground attack and anti-shipping purposes. It wasn't really for defense as much as offense. It could angle down more in the gondola, is my guess.