First question with gear choice is: AODE or T-5? If you have an automatic, the dogmatic answer is 4.10, and 3.73 for a stick.
From that, you need to think about what you want to do with your car, and what you might do down the line. If you are thinking of leaving it pretty stock, as you have it now, then go lower (higher numberically) or at least with the suggestion above. But if there is a big power adder (blower, turbo, etc) or HCI in your future, then you might want to lean toward a higher ratio (lower numerically). For most guys who street drive their 5.0, the gear ratios to consider range from 3.55, 3.73, 3.90, 4.10 and 4.30.
Highway cruizing is essentially unaffected by going up or down a notch in ratios. WOT at highway speeds is likewise unaffected. WOT at illegal speeds will be affected by going with a lower gear as you will max out 4th sooner (5th is not an acceleration gear). But, of course, you are not driving that fast on public roads, right?
All that said, WTF are you doing driving 150 in a 10+ year old car??? Keep it safe dude.