bottlenecked or not you will have massive performance improvement over your GT430. for your resolution you will be able to crank up the setting most of the game out there with ease. your psu should be able to handle the card unless your unit was some cheap generic one.
in regards to botttleneck issue your cpu might bottlenecked the card. from my personal experience my 2.93Ghz (stock) E7500 did bottleneck my GTX460. i not sure how much speed needed to eliminate the bottleneck issue but i did OC my cpu to 3.6ghz
Why would the PSU be the next thing to upgrade? Unless he upgrades the rest of his computer to more power hungry components there is no need to upgrade his PSU at all.
well the 560 takes 150w of power and if he ever want to upgrade his gpu his psu will be the first to upgrade because the newer cards are "power hungry" so he couldnt even use his new gpu without upgrading his psu