Lee, I own both of those engines.

You really can't go wrong with either. Both are manufactured in Japan and are therefore built to outstanding levels of quality. They both start and run well from new and don't require a lot of break-in to be flyable.

The Saito is a little lighter, will pull a heavier prop a little better but will use noticeably more fuel when compared to an OS .91 Surpass. With lighter props (where they are spinning at about 10k rpm) there's not a lot of difference in power. They are both extremely reliable but if I had to bet my life on an engine to complete 100 flights without a single deadstick, I'd lean toward to OS.

I'd recommend buying whichever you think looks the coolest.

It sounds like you have a fantastic LHS.

Good luck and don't forget to file a maiden flight report!