Security mode throughput
The 350N had wireless security-enabled throughput loss similar to the 600N's. Figure 10, taken with the 2.4 GHz radio running uplink in 20 MHz channel mode, shows a loss of about 40% for WEP and WPA-TKIP modes and no measurable loss for WPA2.
Figure 10: Security mode throughput comparison - uplink
Figure 11 shows downlink loss for WEP 128 and WPA-TKIP around 56% and around 10% for WPA2.
Figure 11: Security mode throughput comparison - downlink
From looking at the plots themselves, I suspect that the WPA2 download loss would have been better without the periodic throughput "dropouts".
Throughput vs. Path Loss
NOTE: We don't refer to "range" in these plots, but instead use the more accurate "Path Loss". For an explanation, see the How we Test Wireless article.
Figure 12 was generated using the Compare Benchmarks tool of our Wireless Charts and shows up and downlink performance in 20 and 40 MHz channel modes. Similar to the WRT600N, the 350's 40 MHz channel mode seems to provide a meaningful throughput boost only when running downlink.
Again, note that the multi-second throughput dropout that I mentioned earlier tends to move these throughput values downward. (Each point on the plot is the average throughput for a 1 minute test.)