Currently I have slated two and a half days for siem reap but am reconsidering if that is enough. What are people`s thoughts on skipping the mekong river delta in favor of more time at Angkor?

The usual amount of time to visit all of the major temples is three full days. If you are interested in more, you can easily fill a week without seeing all of the accessible temples. Personally, it would be no contest - I'd save the Mekong Delta for another trip and spend more time in Siem Reap. I found that at the so-called minor temples we were often the only visitors which was magical. But only you know how interested you are in the temples.

some disagree, but i find 3 full days the minimum for siem reap and that is without seeing lots of the temples or the lake...

I agree with previous posts. I spent 3.5 days in Siem Riep a few years ago and I was just in the Mekong Delta for 2 days last week. While the Mekong was very interesting, Siem Riep is in a whole other class. I think it would be very frustrating to have only 2.5 days there. You need at least 3 or 3.5 to be able to do it at a reasonable pace and really absorb the incredible history and spirituality of the place.

We spent 10 days in siem reap, and we still didn't do everything we wanted!
We spent 4 days at angkor itself, and then numerous trips out to the flodded forest, koh ker, beng mealea, bantay srei etc. wouldn't have done anything differently!