At low set pressures, like the case we're discussing, it's inherently more difficult, and sometimes impossible, to satisfy the 3% rule. 3% of a small number is a very small number.
When you have problems meeting the 3% rule, consider these two low-cost options (listed below) before you consider more costly field modifications. The first one is actually a no-cost option, aside from the cost of doing the engineering analysis.
(A) Engineering Analysis (API 520 Pt II, 6th ed., 7.3.5 - 7.3.6): This is an equally acceptable and compliant way to evaluate PRV stability. It's an alternative to the legacy 3% rule. If the installations pass the Engineering Analysis, then no changes are needed. Obviously this is the first option to consider. You said you're working with Siemens on this design. I know that Siemens is knowledgeable about this API 520 Engineering Analysis procedure. Ask them to perform this analysis to see if the existing installations are acceptable.
(B) Restricted Lift (API 526, 7th ed., Annex E): By restricting the stem lift, the PRV's rated capacity (the capacity used for pressure loss calculations) can be reduced to a user-defined value which is high enough to satisfy the required flow but lower than the rated flow of the existing orifice (at full lift). There's a worked example problem in Annex E that illustrates the usefulness of this design option. If a lift restricter can be installed in your existing PRVs (check with manufacturer), then the cost of this solution is very low.
And, here are some comments on the three alternate designs you listed:
(1) The larger valves, such as the 8T10 valves mentioned, are more likely to experience inlet pressure drop problems. That's because the valve body area (for API 526 PRVs) doesn't increase in proportion to the increased area of the orifices which fit into these valves. Essentially, the larger API 526 PRVs are too small for the orifices that fit into them. Thus, these larger PRVs are more prone to experiencing inlet and outlet pressure drop problems.
(2)Insufficient info about this option. There isn't enough information to allow for informed comments.
(3) You didn't specify whether you're referring to integrally sensing pilot valves, or remote sensing pilot valves. Remote sensing pilot valves will definitely solve your inlet pressure drop problem, because the pressure drop has no affect on the stability of the valve. High inlet pressure drop has no affect on the stability of the valve. That's because the pilot is sensing the pressure inside the vessel rather than the pressure at the inlet to the PRV.