The first thing to read should be Bytors guide on omega as you will find a couple of reviews on the railmaster and the aquaterra. The larger ATs are not very acurate as the case is too thick and i have never seen one with any thing other than cheep asian movements, i have had 3 so far and given them away.
The 39mm has a perfect case because i have both the rep and gen and have mesured it and even swapped the case backs to see if it fits and it does, the rep crystal can be slightly more or less domed than the gen but it is only visible when you compare both. You can find these with the correct case back with aqua terra engraved fitted with eta 2824/36 and seagull st 18, the ST 18 looks more acurate than the 2824/36 versians due to the fact it is a copy of the ETA 2892, the base movement to the co-axial works fitted in the AT.
REP 39mm
gen 39mm on rep smp bracelet
Notice the different gold used, the gen uses rose gold and the rep yellow, If you want to know how good the rep strap is wait a couple of weeks and we will see if the omegaq service center works it out as my wife took her gen in with a rep AT bracelet fitted, hey if they tell me it is a rep i will just blame ebay.
The railmaster is just a top watch if you get the 2006 versian with the better dial.