According to law it is evident that even with an approved EB-2 case, you have the option to file the I-140 under EB-3 – that's a choice open to you, and no one can dispute it. However, this doesn't mean that your I-140 and PERM are permanently tied to EB-3. What is typically done is filing the I-140 under the category that offers a more advantageous date. For instance, if you are in the EB-2 category and the EB-2 date is more favorable, you would file under EB-2. Conversely, if EB-3 is more beneficial, you would choose that option.
It's important to note that you cannot upgrade from an EB-3 PERM to an EB-2 I-140, but you can downgrade from an EB-2 I-140 to an EB-3 I-140 – or the other way around, downgrading from an EB-2 PERM to an EB-3 I-140.
So, when you have an EB-2 PERM, you have the flexibility to file under either EB-3, EB-2, or both. Importantly, this filing of the I-140 does not terminate your case or prevent you from returning to EB-2 in the future. Thus, there's no compelling reason not to consider filing under EB-3. As for whether it's better to file your case under EB-3 or EB-2, my recommendation would be to file I-140s for both categories – EB-3 I-140 and EB-2 I-140. However, for the I-485, it's advisable to file with EB-3 – that's likely the most suitable course of action.
I was very lucky to have Rajiv Khanna's team file my application because the person who worked with me was very patient, very detailed, very sensitive to my concerns. Moreover, she provided me with upto date information on my processing and made every effort to dispatch any material to the INS as soon as possible. I would happily recommend her to anyone.