Your original post has a GTX760.
Boards similar to yours are not listed as having problems on https://spreadsheets.google.com/spreadsheet/pub?key=0AgN1D79Joo7tdE9xMUFlMEVWeFhuckJEVF9aMmtpUFE&gid=3
so I'd think you should be able to OC. How much, as you may have surmised, is a crapshoot, but 3.8GHz seems reasonable, and you may well break 4.0GHz. Just watch your temps, and you may want to get an Antec Spotcool to cool your VRMs since liquid coolers don't do much for them.