bowhunterb_3,
Congrats on the Wasatch archery tag this year. My Brother-in-law drew the same tag, so I will be spending quite a bit of time on the unit helping him as much as possible this fall. I think your goal is reasonable and it is certainly an individual thing, however, I personally would not pass up a good 320-330 bull with a bow on the Wasatch (especially if you have never killed a mature bull before). You will likely see a few bulls pushing the 340+ mark, but they are not all over the place.
As I am sure you are already aware, your "real" opportunities to kill an animal with a bow (within shooting range, not get winded, etc)are so limited that you can't afford to pass on bulls in the 320 range on that unit if you would be happy with one of that size because the bulk of the bulls you will encounter are in that range. If you would only be happy with a 340+ bull and are ok with the possibility of eating tag soup, then by all means hold out for a bigger bull because they are certainly there if you hunt hard, but you may not get enough opportunities with a bull of that size on the unit to seal the deal with archery equipment. Just my opinion.
Best of luck - I know for sure you will have a fun time no matter the outcome and it is a great year to have an archery tag with the hunt going to the 17th of September.