What gems give what stats? Check this out.

[[ Ruby ]]
+1 [Strength 05]
+2 [Strength 08]
+3 [Strength 11]
+4 [Strength 15]
+5 [Strength 20]
+6 [Strength 25]
+7 [Strength 35]


[[ Emerald ]]
+1 [Sense 05]
+2 [Sense 08]
+3 [Sense 11]
+4 [Sense 15]
+5 [Sense 20]
+6 [Sense 25]
+7 [Sense 35]


[[ Saphire ]]
+1 [Concentration 05]
+2 [Concentration 08]
+3 [Concentration 11]
+4 [Concentration 15]
+5 [Concentration 20]
+6 [Concentration 25]
+7 [Concentration 35]


[[ Garnet ]]
+1 [Dexterity 05]
+2 [Dexterity 08]
+3 [Dexterity 11]
+4 [Dexterity 15]
+5 [Dexterity 20]
+6 [Dexterity 25]
+7 [Dexterity 35]


[[ Periot ]]
+1 [Attack Speed 04]
+2 [Attack Speed 07]
+3 [Attack Speed 10]
+4 [Attack Speed 13]
+5 [Attack Speed 16]
+6 [Attack Speed 20]
+7 [Attack Speed 25]


[[ Topaz ]]
+1 [Intelligence 05]
+2 [Intelligence 08]
+3 [Intelligence 11]
+4 [Intelligence 15]
+5 [Intelligence 20]
+6 [Intelligence 25]
+7 [Intelligence 35]


[[ Diamond ]]
+1 [Attack Power 07]
+2 [Attack Power 10]
+3 [Attack Power 14]
+4 [Attack Power 20]
+5 [Attack Power 26]
+6 [Attack Power 32]
+7 [Attack Power 40]


[[ Pink Opal ]]
+1 [Defense 07]
+2 [Defense 10]
+3 [Defense 14]
+4 [Defense 20]
+5 [Defense 26]
+6 [Defense 32]
+7 [Defense 40]

Hope this helps.

Goodluck