+DEX on tank, you're terrible
CON increases Stun resistance, gives HP + CP, weight bonus...
I took a level 80 SK and compared stats between -8CON +4 STR +4 DEX to +5STR -3DEX -2CON
Critical Rate : 159 - 153 -> So that's 6 critical difference...
Attack Speed : 447 - 420 -> Wow 27 attack speed more lol.
Speed : 143 - 135 -> That's probably the only notable advantage, 8 Speed difference
Evasion 108 - 105 -> 3 more Evasion... not really worth anything
HP : 3289 - 3911 -> 622 HP Less, big loss.
CP :1973 - 2346 -> 375 CP Less, so VERY CLOSE to 1000 less HP for pvp...
You NEED the CON for Tank, but not enough to go +CON because you do need the STR for critical damage and attack power. IMO -8CON is worse way to set dyes for tanks.