How much psu power is needed for asus gtx 750 ti and also plzzz tell for gtx 660.My current specs are i5 ddr4 ram nd psu of 240 v nd that to of astrum , plzz also recommend me mid range psu box as i dont have much money to spend on it ( if there is need to upgrade it). Should i go for asus 750 ti or zotac gtx 660 .Thank you