I have the 3.29s on the Bonneville. I did suffer about 1-2MPG loss...but overall it makes it get up and go; especially on the highway. 3rd gear doesn't feel like a dog.
FWIW - Dave built my trans in my SSEi. Along with the base build I went with the 4340 input shaft, stock stall convertor (I had a higher stall and found that I didnt like it. Plus my trans temps were higher.) and 3.29 gears. I also had him install an upgraded ZZP pump shaft and ZZP gun-drilled output shaft both of which he said weren't really needed.
Anyway, if you go with Dave you won't go wrong.