This is the kind of review that keeps me renewing my membership each summer. I appreciate you taking the time to test the bivy in varied conditions, and sharing your impressions on standard sizing, eVent vs cuben floor, and seam sealing vs taping.
After a lot of deliberation I placed a custom order for an eVent Soul bivy last November in long, extra wide (82" shoulder, 68" foot girth) with full length zip and cuben floor. I bought it primarily for winter use under a tarp, and wanted enough extra girth to avoid compression of a winter bag. Total weight came in right at 16oz. The first time out I used it in a snowstorm that my tarp couldn't keep at bay, and it came through with flying colours. So far I've used it in temps ranging between 10-25F, and I haven't noticed any condensation on my bag or inside the bivy each morning.
Regarding seam sealing vs. taping, my understanding is that the latter would add about 4oz to the overall weight if it was offered.
Ron was great to deal with throughout the custom ordering process. I wouldn't change any of the specs if I were to order this bivy a second time. I appreciate the extra space on long winter nights, and the ease of access with the full length zip.