Ungemmed, the prae's legs have 1.85% dodge, 1.82% parry, and 18hit.
Ungemmed, the sunguard legs have 1.85% dodge, and 2.18% avoid from defense, and 23 expertise.
Ungemmed, the unwavering legs have 1.16% from defense, and 59 bv.
The sunguard legs have 3 more sta and 0.36% more avoidance. If you popped in 10def/10def/10dodge in your prae legs, you'd pick up 1% from dodge and 0.52% dodge, giving you 1.16% more avoidance (less the gems from your prae's, for about 1% more).
So, you'd gain 1% more avoidance than your current piece, and lose a bit of stamina, and trade 18 hit rating for 23 expertise (not a HUGE loss, but a loss nonetheless).
Personally, I say it's worth it for an avoidance fight if you have the gems available, but I myself wouldn't because epic gems aren't easy to come by for me.