Here's some food for thought... let's say you do get a 2 MPG increase by switching to manual hubs, and you normally average about 16 MPG with your VX, and you drive 10,000 miles per year, and gas prices average $4.25 per gallon..... that's a savings of about $295 in just one year (so the hubs pay for themselves in about 4 months).

I just got mine installed a couple of weekends ago and personally I really like them. The handling really isn't much different and the acceleration feels a little less restricted, so if I get a 2 MPG savings to boot, I have no complaints.