Personally, I tend to think that fitting the HUD to the cockpit avionics to achieve a "gauged cockpit" look is somewhat hackish anyway. No offense, but HUD is not supposed to be like that. Also, it will fail hard as soon as one turns their head in the cockpit just as much as it will with different field of view settings.
I would rather just have the cockpit have good-looking static or slightly animated panels, with an option of putting in render-to-texture gauges/displays when that particular feature gets put into the engine, and leave the HUD what it most likely is; a helmet-mounted head-up display.
Also, yes you would notice the difference between fields of view. Particularly when you turn your head. There would be a difference in angular velocity of outside and inside rendering when the point of view is in turning motion. This would especially affect anyone willing to use TrackIR, but would also likely be noticeable with how the left/right/up/rear views work at the moment.
chief1983: That sounds interesting and promising...