We usually have the basses start with extra "alleluia" alone, before all parts join in (i.e. as written in the Snogbook), though we'll vary that with local customs (e.g. I believe in Southron Gaard / Christchurch, it's usually done with the basses singing two preparatory "alleluia"s). We then usually repeat back to the place where all parts join in, to sing the song twice altogether.
Speed is pretty variable: slow, moderate or very fast, depending on our mood.
Dynamics for the upper lines: the upper lines alternate between phrases with words, and phrases with just "ah". We usually emphasise the phrases with words, and pull back a bit on the "ah"s. This brings out the words, and creates a nice alternation between the voices, especailly when we're singing one voice to a line.
- Big Lochac Snogbook, page 10.
We sing this as written, or anything up to a 5th lower.