“The 6 Plus isn’t just larger — it has a higher resolution (1,920 x 1,080 vs. 1,334 x 750) and a higher pixel density (401 pixels per inch vs. 326 ppi),” Lynn La reports for CNET.
“The 6 Plus will be able to use special iPad-style landscape modes on some apps when the phone is held horizontally; the 6 will not,” La reports. “Only the larger iPhone 6 Plus has optical image stabilization.”
Lah reports, “The 6 Plus has a higher battery capacity [iPhone 6: talk time up to 14 hours on 3G and Internet usage time up to 10 hours on LTE, iPhone 6 Plus: talk time up to 24 hours on 3G and Internet usage time up to 12 hours on LTE].”
Full iPhone 6 vs. iPhone 6 Plus specs comparison here.