Don't get a Taller trans, I'm sure you will be happy with the LX trans, as I believe it's 3.73. 6mpg would probably be on the low end, that's only a 30% increase. If you have appropriate tires and keep your speed at 70mph or lower, 50 should be possible. At least 45. If you want, you can go the Taller geared trans from the VX/CX and lower your tire size to P165/65R14 Bridgestone potentza Re92's. Then you will definitely get 50mpg easily.
[Edit]: Your car will probably look silly with such small tires, but you are driving this for mileage and gas savings, no?
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