Buildings with Non-Standard Space Temp/Humidity Conditions

I am working on an archive library that requires 50F and 35% RH indoor space conditions. The HVAC system in the proposed design is quite complex to maintain these conditions and includes a regenerative desiccant wheel, gas furnace to obtain high temperatures for the wheel, cold chilled water temperatures (36F), etc. This system is designed to deliver 25F dewpoint. Appendix G defines the baseline system as System 5, but I may be able to apply an exception to use System 3. The proposed design is not part of a district energy system so the cooling type is DX. Appendix G states that space temperature and humidity conditions shall be consistent across the proposed and baseline designs. My question is what efficiency do I use for the baseline HVAC system? No systems in Table 6.8.1 of 90.1-2007 seem to apply. I understand that the baseline systems usually do not make "realistic sense", but if I am to use minimum efficiency requirements in Table 6.8.1 then there is no hope for energy savings. Your advice and experience are much appreciated!