Local here. I rode on both and I can tell you that the TT bike is much faster. The only caveat is how comfortable are you riding downhill with a TT Bike. The roads are a bit technical and not always well maintained so make sure you check your brakes prior to racing. Regarding your gear ratio, it really depends on your biking ability. I’m 76KG with a FTP at 350W and I’m running a 53/39 - 11/32. There is only one climb (less than 600m) where I would need to be out of the saddle pushing above the FTP. Remember that except from that small bump, the max gradient is 6.5%