1. Can I make an OVERDIVE with LESS than the MAX OVERDIVE speed?
As I read it, you can only do an overdive with exactly the max overdive speed; not more, not less.
The way I read it, the Max Overdive Speed is the new speed limit for the dive. Similar to Maximum Dive Speed being a speed limit.
Here is a Q&A I pulled up from the General Magazine. I don't know if it sheds light or not, it is included just for consideration:
Q. Can you dive at overdive speed while only
diving within your maximum dive limits?
A. Yes, it's considered an overdive (because of
velocity), even though the aircraft is diving
beyond its normal dive (altitude) limit.
2. The rules say, that "standard" accumulated damage only takes effect AFTER the defensive fire phase. A doomed plane can therefore return fire before it chrashes.
But in the tournament rules for critical hits, it is stated that criticals take effect IMMEDIATELY(!).
That seems to imply that criticals affect the plane BEFORE the defensive fire phase, right?
I looked it over, I don't think immediately supersedes the simultaneous nature of the combat described in the basic rules. I think the rules are implying that the effect kick in right away.
3. Is there a deflection modifier for rear-firing machine guns?
Wow! Deep into the optional rules we go. I would say 'yes'. The rules don't specify so it seems like it would apply to all machine gun fire.