Fully updated post, silly edit time limit:
274 > 238
274 vs 238 Quick Specs
Worked Penetration: 280-295 vs 280-295
Four Ball Wear Scar: 0.6mm vs 0.63mm
Four Ball Weld Point: 315KG vs 400KG
Water Washout % loss: 5.4% vs 5.5%
Timken EP Test: 60lb vs 65lb
Oil Seperation: 2% vs 1%
Evaporation Loss: 0.25% vs 0.25%
I've used both, I greatly prefer the lower rolling resistance of the #274, and if I didn't have a case of 197(that is going to be with me forever lol ) to use, the 274 is what would be in my gun. If you want to be cheap or need something that requires very high pressures, use 238.
If you don't mind spending a bit more, you can always look at Redline CV-2 grease, it's awesome stuff, but $15 a tube does get pricey fast.
Just of note from the TDS of 238:
Due to its superior cohesive and adhesive properties Ultra Supreme is not recommended for use in passenger car automotive wheel bearing and electric motor bearing.
Schaeffer's Quick Notes:
238:
•An upgrade version of #221 with extra tackifier, extra solid lubricants and synthetic blend base.
•Steel industry, mining and construction equipment.
•Extra MoS2
NLGI #2 0° to 350°
http://www.schaefferoil.com/238-supreme-grease.html
274:
•Use one grease Summer and Winter.
•Synthetic blend base eliminates changing grades.
•Versatile, multipurpose, extreme pressure.
•Steel industry, mining and construction equipment.
•MoS2
NLGI #2 -20° to 350°
http://www.schaefferoil.com/274-synthetic-grease.html
Technical data sheets:
238:
http://www.schaefferoil.com/cmss_files/attachmentlibrary/TD Sheets/238.pdf
274:
http://www.schaefferoil.com/cmss_files/attachmentlibrary/TD Sheets/274.pdf