There is no way to avoid the Outlook msoNormal gaps on forwarding to Gmail. Here is an interesting article on the topic.
There are ways to limit it's effect though. The gap created between tables is bigger than the gap created between table rows. As you have rows, you are already experiencing the lesser.
The easiest fix would be simply combining your rows into one row with <br>
's separating the lines of text.
Example:
<table width="600" border="0" cellpadding="0" cellspacing="0">
<tr>
<td width="100">
address<br>
phone<br>
fax
</td>
<td width="500">
: your address<br>
: your phone<br>
: your fax
</td>
</tr>
</table>
This may also have something to do with the min <td>
height. Outlook has a minimum height of 19px, so anything smaller can create unwanted vertical space. There are some line-height hacks, you can try to work around this also.