For starters, ifixit has their compatibility mixed up a bit on these ranges. There is no such ranges as an Early 09... there was a Late 08, then a Mid 09 (but there was 2 versions of the Mid 09, which is probably where they got confused)
Regardless of the exact range, as both the 08 and 09 models use the same ram modules and have the same upper limit, you will need the PC3-8500 modules.
You have 2 slots on your machine, and it does support interleaving (which means they will function faster if both modules are of a matching capacity, because it works in a similar way to a raid unit. it stripes between the two, so although you can fit two different capacities, it will function more efficiently with two matching capacities)
Your upper limit on these two models is 8GB in total, so split that between two slots with 2x4GB modules.
i hope this helps