How does the iPhone 4 (CDMA/Verizon) speed compare to the iPhone 4 (GSM/AT&T) model? Which is faster?

Please note that the iPhone 4 has been discontinued. However, this Q&A has been updated subsequently and can be quite helpful for anyone buying or selling either model on the used market.

In most respects, the iPhone 4 (GSM)/iPhone 4 (GSM, Revision A) and iPhone 4 (CDMA) provide identical performance -- boot time, running applications and uploading and downloading data over Wi-Fi essentially are identical. For these tasks, the answer to "How much faster is the iPhone 4 than earlier iPhone models? How does it compare to the iPad?" is applicable to both models.

However, there is a notable speed difference in uploading and downloading data over the respective GSM and CDMA wireless networks.

In an in-depth review from the always excellent iLounge, the site reported that:

Whereas our AT&T iPhone achieved cellular download speeds in the 2.6Mbps range over AT&T’s network -- and we're not in a location with particularly impressive AT&T 3G towers -- our Verizon phone struggled to achieve 1Mbps download rates from the same indoor testing location, most commonly seeing speeds in the 0.6 to 0.8Mbps range, with both phones floating around three bars of stated signal strength. Verizon upload speeds averaged 0.4Mbps range relative to AT&T speeds in the 0.8Mbps range. Outdoors, we went to a location where both phones showed five-bar signal strength, and though AT&T’s speeds were similar to what we saw indoors, jumping into the 1.1 or 1.2Mbps upload speed range, Verizon's performance improved to an average of 1.5Mbps for downloads, once hitting nearly 2.2Mbps, an aberration relative to other results, while upload speeds fluctuated in the 0.7 range.

While both phones were subject to significant variations based on testing location and the location of the servers they were connecting to, the AT&T iPhone 4 was most frequently faster than the Verizon version, sometimes by a significant 2:1 or greater margin, and at other times roughly matching it.

To help visualize this speed difference, videos often can be quite useful. This pair of videos, from Zollotech, show the iPhone 4 (GSM/AT&T) model on the left and the iPhone 4 (CDMA/Verizon) model on the right. The first video is using a benchmarking tool and the second video demonstrates the speed difference loading web content in real-world use.

iPhone 4 Models (Network Benchmark Comparison)

iPhone 4 (Real-World Browser Comparison)

iPhone 4 Network Performance Summary

Ultimately, the GSM-based iPhone 4 is significantly faster uploading and downloading data over a 3G network than the CDMA-based iPhone 4, which uses an older -- and slower -- wireless networking standard. However, in the US, Verizon has the reputation for being more reliable, and if this is your experience in your area, you may -- or may not -- find reliability to be more important than speed.