Are these the old style levers that were only brake levers and the shifters are on the downtube? If so, and you are going to spend money, then get proper STI's and then you'll have a more comfortable hand position on the hoods.

A flat bar is only going to give you less choice of hand positions. And the one it does give is not a good position if you are actually riding for time and distance... IMO. Being able to change up positions is part of keeping your hands and wrists from having issues on long times in the saddle.