I have been overclocking for years (I mean a really long time, as in I overclocked a P5/200 to 225 mhz by running the FSB at 83mhz... before ANYONE was overclocking) and if there's one thing you learn about o/c it's that not all chips will do a given speed. Regardless of the core, the stepping, etc, etc.
Especially with manufacturers binning their parts (in other words testing and selling the higher performing parts at higher speeds) it is difficult to know that what you are buying can overclock at all.
If you really wanted 1.4 gig you should have bought a 1.33 gig part. It's more likely that a 1.33 gig part would be able to do 10X140fsb and probably would be stable. Also you wouldn't have to void your warranty by unlocking it.
There's probably lots you could do to continue your o/c adventure. People have had to replace half their system to find out why they couldn't hit a certain speed. RAM, power supply, motherboard, heatsink and the chip itself are all suspect. The funny thing is you can easily spend more on this approach than it would have cost you to just buy the higher end part in the first place.
When a 700mhz part cost $250 and a 933 mhz part cost $500 I could understand the drive to o/c. But now that you can get any speed t-bird for under $200 I don't see what the big deal is, people try to save $50 and rip their hair out in the process.
It's too bad your part won't o/c, but then again, you got what you paid for.