Can you negate/notch all other than what plat. Might come up as? For instance, with my Garrett AT Pro you can isolate specific target ID numbers while excluding all others...if u have some target metal to use to begin with....ie, you swipe a gold ring at "x", then negate everything else so as to only have similar gold rings sound....seems would allow u not to waste too much time digging tabs.....(My wedding band is 30gm .960 Plat with 8 stones, and pulls a strong tone at just 4 on the VDI....FYI.)
I have a whites V3I too, but haven't delved to deep into the expert menus yet...they must have exclusionary modes though your mileage may vary....

Good luck....
cleansweep, the trouble with this notion is, that it assumes that platinum has some certain numbers that it "might come up as". That's where the trouble starts, is that there IS NO certain numbers that platinum comes up as. Well ...... kinda. Here's the deal: It depends on the size of the object, NOT the "type metal".
For example, take aluminum for instance: most md'rs will tell you that aluminum (foil and tabs for instance), are "low conductors", right? HOWEVER, if you take an entire aluminum can, and wave it in front of your coil, what does it read out as? A penny or quarter or something, right? (ie.: a high conductor). But notice the composition of the metal in each case (a tab verses an entire can) has not changed. In each case, the item is still the same material: aluminum. So what changed then? The SIZE. So too is the logic the same for platinum or gold, etc.... If the ring was a big honkin man's ring (college ring sized, for instance), I bet it could read up as high as zinc penny, even though platinum. But if it is a dainty ladies solitaire, it might read down in the low foil range.
So the OP is going to have to have an idea of the size ring he is looking for. Once he does, then yes, he can "play the odds" and edit out #'s that it's not likely to read at. However, even then, that presents a risk: Because as we all know, in actual field conditions, there can be stray bounces that any target takes. So if you're first swing over the target happens to be one of those "stray bounces" on the TID scale, you would risk having it disc'd out. So if hunting for something like a gold ring (which might not even give a consistent locked-on TID anyhow, if it's not perfectly round), the searcher should open up his disc, and then evaluate each signal on a case-by-case merits, letting his ears do the work, watching the cursor, etc... Then sure, he can skip the "obvious pennies" or the "obvious nails", etc...