your last statement
cleared up the detail I was not considering, namely that even though A5 has a similar advantage to hilo at a similar count, that count will happen far less frequently since so few cards are being counted (A-5 only).
For fun, I set this up on CVBJ and played for about 15 minutes using this count. It was pretty interesting in that there was one stretch of 8+ hands (heads up play) where the count never changed as no ace or 5 showed up.
Going the other way, I had thought about changing from Hi-Lo a couple of years back as I discovered systems with better PE, but some simulations I ran (custom software) convinced me that the advantage for changing would be minimal, particularly as at the time I was mainly playing shoes. Probably if I were traveling the world playing blackjack, I'd give this serious thought. But playing mainly in the SE with a trip to Vegas here and there, hi-lo seems to be serving me well.
I'm heading to Vegas early in July, and am going to pay more attention to downtown this time even though we are staying on the strip. Planning on seeing what kind of SD/DD games I can find downtown (if any) with decent penetration.
Thanks for the non-argumentative discussion, that is becoming a rare thing to find. :)