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Chris, My daughters focus is using 5w-20w we live in Ontario, Canada.
We have had no problems in the hot weather(Low 30's). Her driving is much
like yours. It won't hurt to use 5w-30 in the summer if it makes you feel
better.
I did read that in some States 5-20 is not available and Ford dealers use
5-30.
Geoff.

I was just reading the owners manual for my new Focus ZX3
and it says "SAE 5W-20 premium synthetic blend motor oil (US)".

The 2000 model of the Focus oil recommendation was 5W/30.
On the 2001 model the oil recommendation was 5W/20.
For about 9 months in 2001 the Ford dealers were unable to do an oil changes
with 5W/20 as the oil was not available, so they used 5W/30.
I contacted Ford on 2000 when I purchased my 2001 Focus and they told me
Exxon/Esso was the supplier of this oil grade. I contacted Exxon/Esso and
they said that they had no future plans to retail this oil grade.
The reason that Ford went to 5W/20 was to improve the CAFE requirements for
fuel economy.
It was nothing to do with redesigned engines or new technology, it was to do
with Federal fuel efficiency requirements. Ford also recommended that most
models of their vehicles( Mustangs and high performance engines exempted)
from 1998 could use the lighter oil.

For your temperature requirements and road usage 10W/30 might give better
protection than the lighter grades..

I still have trouble finding 5W/20 in western Canada so I gave up using it
and went with  5W/30 as my standard. I can get 5W/20 from the local Esso
bulk dealer and I sometimes see it in Wal-Mart.\ but what the heck its too
much trouble.

I think if you went to a 5W30 oil instead of 5W20 it would be good enough.
Ford sez they use 5W20 due to compression in the engine and 5W30 is not alot
heavier as is 10W30.