Hi, thanks for the added info.
The 30T cog is right about the limit for many Shimano road RD made through the early 2000. Some of the newer ones are supposed to handle a slightly bigger cog. I hope that others will chime in with their experiences. For road derailleurs, I like the 5500 & 6500 series and these are available in a GS (mid-cage) version which will easily handle the total capacity but I'm not sure about the 30T cog clearance (anyone???). I use the short cage on my road bikes and GS on my MTB but don't use any large cogs on any of my bikes.
MTB RD usually have a different configuration to give the upper pulley more clearance for larger cogs. I have used XT & LX level MTB parts and found them to be quite good.

The Tri-color mentioned above is the next generation from the 600EX & works well, but did not come in a GS from what I can recall.

Hopefully others will have more info.