Swapping MB in a Dell is just looking for trouble. They use non standard front I/O wiring and I/O panels. They add and remove things like warning lights and temperature sensors and don't publish the pinouts. Dell builds enough of each system that they don't worry about parts interchngeability.
Here are some Vostro 460 builds.
http://www.userbenchmark.com/System/Dell-Vostro-460/3605
Ijust looked at the Vostro 460 PSU and it comes with a 6 pin PCIe cable and is 350W. so no problem there.
The GT1030 is lame.
http://www.tomshardware.com/reviews/gpu-hierarchy,4388.html
You can swap MB and OC all you want and it won't change that.
if you really want 1080P and high FPS you need a GTX1050Ti or better.
You need more RAM also, 8GB is...