I have an Rogers black 920 (RM820) running on Wind Mobile (Canada, HSPA on AWS), and just flashed to Rogers 1314 (was previously on the EURO DEV 1308 rom). Huge improvement in connection speed.
On both the 1308 Rogers and the 1308 Euro roms, my data speeds in Toronto were slow and the connection flaky. Less than 2M down and 0.1M up on speedtest.net.
Now on 1314, installed, got MS account over WiFi and installed Nokia Access Point to get Wind APN, and it still seemed sluggish. Set the highest connection speed from LTE to 3G, restarted, and went outside.
The phone took a little while to find a network tower after booting up, but now it is doing a new thing: the icon at the top right shows "4G" and when it does, over 6M down and over 2M up on speedtest.net. Occasionally it drops back to "3G" and is slower, but when I try to load something data-intensive it bursts up to "4G". On the 1308 roms it was always "3G", always slow.
I think "4G" = HSPA+, and "3G" = UMTS, at least on Wind Mobile - since they don't have an LTE network yet. And I think the connection issues many have experienced with the 1308 ROMs - on Wind, if not on other networks - have been based on an inability to reach HSPA+.