Stick with this:
A- Powered (45L)
B- Dummy (45A)
B- Dummy (45B)
A- Powered (45C)
That is how they were delivered from EMD and Santa Fe made every effort to keep the together while they were in service.
Also with this configuration the two powered units contain the sound and it will be more evenly distributed as the lash-up passes. 
BTW, I have the full 12-car GGD El Capitan set on order and will probably use the above units for 50% of the time on the El Cap. The other 50% will be Alco PA's either A-B-A or A-B-B-A.
SFJim,
Thank you for your input. I really like the 45 Setup. Also, I was planning on running the Legacy Alco PA's, but the lionel top 10 dealer I was going to buy them from, lost them. They are not sure what happened to them. I had them on layaway. I grew up admiring both F Units and the PA's. I have always wanted to own a pair in Warbonnet livery, and had been looking forward to putting them at the front of the El Cap. Guess I'll wait till the next Legacy revision is announced, as I never see them on the Buy/Sell Board nor even on Fleebay.
Thanks SantaFeJim!
I don't want to jack this thread. I appreciate the link you posted. I am using my CAB2 to build my F unit consist. The display really simplifies building a consist, another reason I love Legacy. I used the ERR Cruise Commander Manual v4.1 to program each engine for Cruise, Large Motor, and 100 speed steps. Then I attempted to use the Nudge feature to speed up the slower engine...didn't work. Then I used the nudge feature to slow the faster engine....didn't work. So I don't know what I am doing wrong. The engines will not match speeds and fight one another when running.
I was very interested in the thread Mr. Muffin started about the Atlas F7s and especially interested and impressed with Jerry Kimble's posts.
I am over a barrel because I am confident these Atlas F units will look stunning. I too considered the 45L-45A-45B-45C to be the ideal consist for my needs (2 powered cab units). BUT, given the troubles my UP F3s have given me I am gun shy.
Everyone seems to report that Atlas engines run well, I am hoping I will have the same opinion. I have talked to Bill Seratelli from Atlas. Hopefully he will help me sort this out, because I would like to purchase the same consist you are buying.
thanks again for your post and to the OP I apologize if I am jacking your thread, maybe this info will benefit you
T4TT,
You are not hijacking this thread. Any and all relevant information that is being shared is mighty fine by me. I had a lengthy conversation with Steve/ Mr. Muffin today (4 Feb), as it relates to the running/ mu of multi-headed loco setup's. During the course of our conversation, he mentioned that he has a very large fleet of Atlas motive power, and has not experienced the issue you are having. He has MU'd numerous trains without a hiccup. Though Steve is a dealer, he is also a gentleman who buys product and runs them, and thus I am willing to take him up on his knowledge and experience, and say I am comfortable with making a purchase. If there ends up being an issue, I'm sure there will be plenty of people, who will be willing to help rectify said issue/ and say I told you so.
Regarding the 3rd Rail suggestions; If 3rd Rail offered Dummy B units to go with their Powered Units, then I would potentially consider the 3rd Rail F7's. However, $2400 is A LOT of money to spend for 4 Powered Units, and though I want an ABBA setup, 4 Powered Units would be way overkill on our layout. We're only in our early 30's, and need to be thrifty on how we spend our money, and not buy on impulse. Once upon a time, I could have spent $2400 on a locomotive purchase, and we would have figured out a way to make it work. As the years have progressed, and our time in the hobby has increased, we have become more aware of what we want for our layout, and how much we are willing to spend.
Dropping $4K plus on a combined setup of Cars & matching Loco's is Lunacy. Though we're in for just a tick over $3K, that is still A LOT of money for us. From a budget standpoint the El. Cap falls in under our 2014 Funds, but I'm not keen on wiping out 2015 on a match set of powered ABBA's, as the year is young. Kyla & I have talked numbers, and we are comfortable with doing the Atlas F7's + El Capitan. When I mentioned the price point of the 3rd Rail F7's, her response was very clear. :-)
