Wow, you live in the land of Still-less-ness. Sad that. Here I get the same BS at some stores, so I go to another one. Many do not know their arses from a hole in the saw. I have found that a lot of saw shops do not know much about saws, or the guy that does is at lunch. I have gone to pro shops and requested chains, and been laughed at or told that I should run something else. I either tell them off, or set them straight, or just go to another saw shop. I am the one with the money, and I am the one running my saws, not them. There are gobs of Stihl shops here in the PNW. I have had a hard time finding RM chain here that I like to run, but I have found it.
3/8 standard 0.050 chain is pretty common around here (in the PNW). 3/8 standard in 0.063 is less common here. I have both types of bars and chains. Either size can be 'pro' chain, depending. Stihl uses yellow and green coding for their bars and chains. Look on the Stihl web site or the Stihl catalog and you will see the different types of chains and bars that they make. Wider nose bars with higher count nose sprockets tend to be yellow, or non-safety bars. They are coded yellow, like your ES 25 inch bar is. That means it is prone to more kick-back than a smaller nose bar which would be coded green. Also chains are coded different, according (again) to the kick-back potential of the chain. Yellow chain tends to have more kick-back poitential than does green chain.
A misnomer here on AS and in some logging and arbor circles is that green bars and chains are homeowner products, and yellow bars and chains are considered pro products. Same with saws; the 290 is called a homeowner saw, and the 361 is called a pro saw. However, I have seen many many pros use a 290 in professional situations, as well as homeowners use a 361. In that sence pro and homeowner mean little, really. As for your situation, ES means it is a solid (not laminated) bar and it has a tendancy for higher kickback. If it was a 20 inch ES bar, it would take the exact same chains as say, a 20 inch E (laminated safety) type bar. Homeoner or pro mean nothing here. For example, I can and do run pro ES bars on my 290 (considered a homeowner saw) with non-safety yellow chains. I also run E type laimated bars on my 361 with RM2 chain (green bar and chain). There is no one to stand there and say otherwise. No saw shop goons should tell you otherwise either.
BTW: here is one of the best charts that I have found on Stihl bars and chains (it is by no means complete though):
http://www.stihllibrary.com/pdfs/SawChainSelection.pdf