Wingman,
I think your talking about the UCD 60 size. My UCD, may it rest in peace had a O.S. 91 Surpass w/pump, it had a 15X6 APC on it. This plane is not going to be a speed demon, it just is'nt made to go fast. It likes to go slow and do nice 3D stuff, with that fat wing too much speed is not good. You don't mention what prop you used on the Saito so it's hard to tell, but Minn's probably right that it's just a bit underpowered from what I've heard about the older Saito's.
As Minn says, lower pitch gives more climb, higher pitch gives more speed.
I would put a 13-4 on the 61, or for more speed a 12-6 or 7.
The UCD is going to be happier with a 91 4 stroke or bigger.