I did the same thing last year on my F85: got 5700 shifters for a good price and they're superb. I now use the MS shifters on my winter bike and they're still noisy, but otherwise fine. They shouldn't be so stiff that it bothers you. You may have the cable tension too high or there may be some friction in the cables or the derailleurs themselves. I recently found the front shifting was getting very stiff and I needed to work some GT85 into the FD and apply some grease to free it up. Works fine now.