Going to a 4-stroke will cause you more issues. The engines you quote are garbage and you'll be dissapointed if you buy one.

Stick with the 1.40Rx and get some help from an experienced user of the engine. It's very hard to fix issues over the net.

I recently sold my Pinnacle with 1.40Rx and it was a very reliable combination. In pattern, reliability is of paramount importance! There's no point having the most powerful engine/set-up if it doesn't finish a sequence.... The OS 1.40 RX while not the most powerful engine in pattern, it is extremely reliable.

This was my set-up:

15% nitro and 18% quality synthetic oil. I used the thicker viscosity oil not the thin stuff they use on YS engines.
I used OS No. 8 and Type F. The F seems to work very well and last longer. Use an F type.
I used an APC 17 x 12 standard prop. Has great pulling power! My engine was doing 8100 rpm on this prop.
I used the standard OS/Hatori Pipe and header. The header had 10mm cut off it and a 5mm gap between the header and pipe. This gives you a reference for pipe length.
Tank was a 14oz Dubro on the CG with an OS one way check valve on the vent line. Stops the fuel running out all over the place from the vent.
Use quality bearings in the engine and leave the rubber seals in place on both bearings. I used SKF and they lasted forever. Cheap bearings will more than likely give you issues.

That's about it I think.

Persevere with the OS. They are a great long lasting engine.

Cheers
Jason.