Oil weight recommendation

[bgm1961]

I've been living in an apartment for the past 15 years and moved into a new house a few months ago. So, I'm new to riding mowers.

I recently bought a Cub Cadet ZT1 50", with about five cuttings behind me. So far, I'm happy with my purchase, and I intend to keep it that way!

My first (5 hr) oil change is coming up. It seems that 10W-30 is the most common/prevalent viscosity sold locally.

However, the Kawaski Engine manual writes: "10W-40 is the recommended oil for most conditions." Of course, it doesn't preclude other weights, calling for them based on the operating ambient temperature range.

So, according to the manual's oil chart:
- 10W-30 is suggested for 14 deg F to 90 deg F ambient temps.
- 10W-40 is suggested for the wider range of 14 def F to 110 deg F.

Where I live in Missouri, the temp often climbs above 90 deg several times during the summer. So, their recommendation of 10W-40 seems the way to go.

BUT:
10W-30 is pretty much the only weight the local stores sell for small 4 cycle engines.
Except, Lowes does sell Kawasaki brand 10W-40! It's the ONLY 10W-40 they sell, and it's the ONLY weight sold with the Kawasaki brand. Not to mention that it's like a $1,000 per quart. <grin>

QUESTIONS:
As such, I wonder if Kawasaki recommends 10W-40 only to help with the sales of their own-branded motor oil (which again, is 10W-40), or if 10W-40 is indeed the best viscosity for 80 deg to 95 deg summer days?

So then, if it's the latter, then why don't the local stores stock more 10W-40???

What viscosity to you guys use and would recommend?

Thanks!