For the price difference of a 5.3 and a 6.0, you would be shooting yourself in the foot with a HUGE gun right now to "save" money with the 5.3. Just think about pricing of cam and heads... I know this price difference vs power difference was DEFINITELY worth it to me.
I have a buddy that has been running a STOCK (ARP rod bolts only) LQ4 with a turbo setup on it in a foxbody, and he just laid down 630rwhp, and has been driving it daily for over a year. There isn't one thing wrong with a rod bolted LQ4 until you are making serious power. He cranked it to 13 psi to race a busa the other day and the motor still purrs like a kittin after 10+ races with the dude.
LQ4 will be your best power per price motor, unless you can find an LQ9 for cheap. Dont waste your hustle with a 5.3, no reason to unless a $400 difference isn't worth some major power to you.
LT1's are tree fiddy chebby motors, and yes, they are, from my personal and multiple freinds experiences, hard to get power out of. Friend with a 70 trim setup on his laid down 446rwhp and 511tq, IMO, look at the difference from that and 630rwhp on the SAME turbo on an LQ4 and that right there would be my eye opener on power potential.