I have both Strike Fighters and Wings Over Vietnam, and see no difference between them. I think the reason that you see more sam activity in w.o.v is that the terrain itself contains more sam sites.
I used to use the drv terain in sfp1 before I got a copy of w.o.v, and that terrain had even more sams and aa guns than w.o.v. It was so bad, that it used to kill my fps and make the game un-playable.
Are you setting your aa defenses on hard? That can make a real difference.
I spent like a whole week just reading all the sfp1 boards on sim hq, thirdwire, here, at frugals, and it helped a lot.
~NPH~