I'm pretty sure that the first one is a Tbred B and the latter is a Tbred A core. The B core is better for overclocking if you're in the know and that may be why it costs more. (I am assuming the first one is the more expensive one)
This is wrong, they are both Tbred B!
Hi! Its the voltage:
... and this is correct :P
To sum up, basically if you are going to overclock (and I don't see the reason why not), go for the AXDA1800DLT3C. It has much better overclocking potential than the other proc you mentioned. Just for the record, I have a AXDA1800DUT3C running at 2GHz (2400+, vcore @ 1.675) so you will deffinetely have much better results (AT LEAST 2600+ speeds). I am using SLK-800, SmartFan 2 @ 3000rpm, Arctic Silver 3 and my temps are 37C idle/42C under load.