To make the top level fluid just remove the width that you have on the list and add some padding or margin to space them out a little.
For the drop down you should never really make elements bold on hover because they take up more space and cause a reflow. You may be able to add padding and then take it away to offset the difference but its still not a good idea.
e.g.
Code:
#topMenu li ul li{
padding:0 13px;
float:none;
display:block
}
#topMenu li ul li:hover{padding:0 5px}
#topMenu li ul li:hover a{
color: #FFF; /* White */
text-decoration: underline;
font-weight: 700;
float:none;
display:block
}
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