Which specific rules of thumb?
When the Hawk first entered service, BWoS wondered why fatigue use was so high. "You didn't use that much 'g' in the Hunter - why are you doing so in the Hawk" quoth one worthy.
"Because we can" was the obvious reply!
Good things about the Gnat:
1. Sooo responsive.
2. Offset TACAN
3. Classic swept wing characteristics
4. It was cool to go supersonic solo!
Bad things about the Gnat:
1. Virtually everything else
Good things about the Hawk:
1. Fuel!
2. G
3. Easy to fly
Bad things about the Hawk:
1. The abysmal compass system it had pre-AHARS
2. No offset TACAN
3. That's about it!
Did Brawdy on the Hunter and then a few years later Chivenor on the Hawk. Each had its advantages - but only one was a true thoroughbred.
Do they still do the TACAN dive to point Alfa, then ILS via point Foxtrot profile at VYL? That might help chummy with his FS2004 query.