Lol, 3x4 feet at 300 dpi? That's 14400 pixels wide!!! What's the print for? For what purpose? That's waaaaaaaaaay over kill for 99% of uses. Even pros wouldn't print at that size, not only that, I challenge you to find a printing process that can actually print that size at in the first place that won't cost you a small mortgage.
Besides, you can easily achieve 4x3 foot at half that dpi with little noticeable quality drop. The relationship of physical image size in inches to pixel size to dpi is generally very confusing to most peeps. And understandably so.
If you say what you actually want to achieve then we might be able to give you sensible suggestions.