So gas on my Durango is kicking me in the teeth so I have to get the Honda back on the road. Its a 94 VX Civic

The clutch is slipping bad on it so I’m going to have it replaced. While the transmission is out I figure I should go ahead and replace it since it makes some really bad retelling noises (think marbles in a coffee can) and reverse is rather hard to get into.

So while I’m putting another transmission in I figured I would consider putting a DX or SI transmission in it’s place rather then another VX one.

My questions are
Would there really be that much of a noticeable difference in stop and go traffic?
Will I get noticeably lower gas mileage?
Can I use the VX axels?
What clutch should I use, one for the transmission I choose or the VX one?
Is there anything else to worry about or that I will need?