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It all depends on your idea of "practical" and what you want to use the truck for. If it's for offroading then you have to take into consideration the kind of offroading you'll be doing. Then you get into tire size, axle strength, etc. so it all depends. 6" is usually pretty decent for a truck that will be street driven daily but used offroad occasionally. It leaves the bed low enough for you to load and unload stuff if you need it to haul anything.
Just keep in mind that for a 35" tire (which will look great and perform well for mild offroading) you'll really want to regear your axles or the truck will be bogging down horribly. A swap to 4.10's would do the trick so your acceleration and power don't suffer.
If you put on bigger tires, then it won't cut down on speed at all. I also have a 300/ 4 spd, and I would recommend 35s with 4.10s. I have 33s w/4.10s and it is a little low geared. It screams at 65. I used to have 3.73s, and that is pretty good with 33s.