The Excelleron with the YS120 was too much (IMO), my friend had to move the servos to the tail to balance it. Sadly it is no more, it suffered a sudden unplanned hard (too hard) landing and a debris picking crew was called to clean up the mess. I got to fly it a few times and I didn't like it very much, it felt heavy, specially when compared to mine with the Saito100. It was very powerful, but for pattern style flying I had to really struggle to make it look smooth, throttle management was too critical. Also landing was kind of difficult (again compared with the lighter one) as you often had to kill the engine to force it down or land it hot. With mine, I just line it up, cut throttle to idle and let go the sticks until it's time to flare, anyone who flies it can put it on the ground on 3 points without any trouble.
Now, the Saito100 is lacking, specially at 4000ft. It is barely enough for Sportsman at this altitude, but last contest I attended was at 4500ft and could not make any tall intermediate maneuvers and my box was severely crippled and climbing was agony.
The YS91 is a bit better than the Saito, but I believe the YS110 would be perfect, unless you intend to do 3D, then go with the larger engines.
But for pattern or sport flying a YS140 in this airframe would be nuts (again IMHO).

My friend that lost the Excelleron now has a Venus II with a YS91 and he is really happy with it, specially since Troy Newman trimmed it, but he will change the engine to the YS110 as recommended by Troy.

Gabriel