Yes, ZEN vision is the BEST! I'd never wear any shades except oakleys. And it helps to have a chio Joey serving you. But alas, she wears a ring...
Oakleys has control price in Sg, so buying at ZEN (which has the widest ranged) should be a good choice, unless you can find a shop willing to you sell you cheaper than RP and keep quiet about it.
One bad thing about ZEN, it closes for lunch from 1-2pm, which I find it to be a stupid excuse to close shop.
I am not sure if Zen vision will be willing to serve you. They are more in charge of warranty and repairs.
I will also let Joey know she has many fans out there... She just dyed her hair purple and brown, did you see???
I think if you wanna touch and feel oakleys without much probing, try paris miki on taka (5th storey i think)
another good shop is on the 3rd storey of taka as well.... good collection of shades there.
as far as i know, oakleys' prices are pretty fixed. if you do get a discount, do make sure their warranty is valid within singapore. you wouldn't want to get them from a banned shop and find out your warranty isn't valid. Alomost happened to me once when I got a pair of twentys from serangoon plaza at 30 percent off last time