I have to say my Mrs would prefer something smaller that came from Tiffany's in Mall at Millenia or another reputable dealer than larger from an outlet store but that's maybe just my Mrs.
Also don't worry about repairs and valuations etc anyone can do those admittedly at a fee but given what you'll save buying outside this country it's worth it.
I got the Mrs a diamond eternity ring from Tiffany's in New York years ago at half what I'd pay for the identical ring over here and a pearl necklace and earrings from Tiffany's in mall at millenia a couple of years ago again for a fraction of the UK cost.
I asked my Mrs to marry me without a ring which we then went and chose together as she knows shed loads more about diamonds than I do. There are diamonds and there are diamonds. A small but high quality one will appreciate in value, whereas a large but flawed one will be worth little in years to come. Not so much for selling it on as everyone would hope that doesn't happen but even for insurance purposes, if stolen the insurance company will give you a pittance for a lower quality diamond ring regardless of the valuation.