The largest 737 operator in the world operates over 315+ 200/300/500/700 aircraft in a common fleet. Southwest Airlines.
I disagree with some of our procedures in relation to automation and the dumbing down of the 3/5/7 fleet to make it compatible with the 200's. We operate without VNAV and autothrottles and have no EFIS 300/500 aircraft. The 700 depicts steam gauges and has a map diplay on the right pilot display unit. The management regularly states that they want our pilots "in the loop" and hand flying the jet and staying in touch with the situation at hand. My opinon is that we could handle the difference and the reason is found in "old school" thinking on managements part.
I flew a "full up" EFIS 300 and both advanced and basic 200 models while at America West. I had little trouble transitioning between the types. I look to the fact that I fly several civilian jets and props on my days off and I seem to keep them straight.....just have to brief the differences before operating them.
The -200's are going to go to a Texas base when the numbers get down to around 25 units for company convienence. We currently operate over 40 units today.