5w-30 vs. 10w-30

Colorado Springs
OH KNOW NOT AGAIN!!! I was looking at Chevrons data sheets and now, the 5w-30 data sheet clearly states it's made with Isosyn basestock, where as the 10w-30 does not. Also, from Valvoline's MSDS, their 5w-30 is group II and the 10w-30 is group I. I'm starting to come around into believing 5w-30 is a superior oil even in hot climates since it's made with more refined basestocks.
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Not Seattle, but close.
I've seen, and bought bottles of Chevron 10W30 that say Isosyn on the bottle. Also, in November of last year, I had an email discussion with a Chevron engineer, who told me that both Chevron and Havoline regular as well as High Mileage oils are Group II basestocks in each grade.
Charlotte Metro area
IF you drive mostly short trips...use the 5-30. IF you drive mostly long trips...use the 10-30...and extend those OCI's. I base this OPINION on reported increased wear at startups due to the oil being so thick when cold, therefore the 5-30 recommendation if you are a short-tripper. The 10-30 might hold viscosity a bit better, and long trips are "easier" on the oil, therefore the 10-30 suggestion, with extended OCI's.
I think at temps above 50 degress F, from a viscosity viewpoint, the performance of 5W-30 vs. 10W-30, is so close, that any debate results in a hair splitting exercise. Looking at market stats, the last figures I viewed for usage indicated that the 5W-30 & 5w-20 combined beat the 10W-30 share, but 10W-30 was still greater than either of the 5W grades on an individual basis. The 10W-30 grade is still popular with DIY oil changers and as a bulk oil grade.
Santa Barbara, CA
SAE Viscosity Grade 	SAE J300 	5W-30 	10W-30 
API Service	                      SM 	SM
ILSAC	                            GF-4	GF-4
Gravity,°API	ASTMD-287	    31.4	31.0
Specific Gravity @ 15.6°C(60°F)	ASTM D-287	0.863	0.872
Flash Point,°C	ASTMD-93	     216	221
Pour Point,°C 	ASTMD-97	     -36	-36
Color	ASTM D-1500 	             2.5	2.5
@ 40°C, cSt 	ASTM D-445 	     63.9 	70.1 
@ 100°C, cSt 	ASTM D-445 	    10.5 	10.4 
ViscosityIndex	ASTM D-2270	     158	135
CCS Viscosity, cP (°C) 	ASTM D-5293 	5,800 (-30) 	5,900 (-25) 
MRV Viscosity, cP (°C) 	ASTM D-4684 	25,100 (-35) 	16,300 (-
HT/HS Viscosity, cP 	ASTM D-4683	3.0	3.1
Noack volatility, % 	ASTM D-5800 	14.7	10.9

Dang no edit button. Anyways you can see the poorly formatted data. 10w30 is slightly better on paper (if you have cold starts often)