Are you talking about the new Nocona based LV Xeons? Or are you talking about the older Prestonia LV's ?
I don't think that the prestonia's ever had an 3ghz LV.. The Nocona's might.
The reason people use the D1 or M0 stepping is that there were some specific chips that had the perfect recipe for great clocks.. Say the 2.4ghz LV D1's or M0's... They had an fsb of 133mhz, and a multiplier of 18. With tricks, you can boot up the chips at 200mhz fsb, but the problem is that Xeons will always POST at FSBxbootstrap multiplier. This means that you need a decent chip with a low multiplier to ever have hopes of running at 200. A 3.06 chip will be 133x23. To post this at a fsb of 200, you will end up running for a few seconds at 4.6ghz (200x23) Ouch. The 2.4ghz chips are the best for this, because a lot of xeons can at least post at 3.6, then load up a new multi.
Now, with Nocona's (naitive 200fsb) you just want a high multi. The LV's will be good, because they might give you more overhead (think Mobile Barton) Crank those volts back to normal, and you might have a nicely clocking chip - problem is, you want a high multi because xeons are still hard to push high into the fsb range. MAX you should be able to reach is around 250.. and thats a big maybe.. So to get really high clocks, you want a high multi.
So.. back to your question: Clarify exactly which chip you are looking at :- ] Nocona wise, LV's will be probably be a bit better than their non LV counterpart.. if the cost is prohibitive, though, go with a better chip with a higher multi :-]