Neither of the standalone films are terribly essential...watching on DVD, you're better off not interrupting the momentum of the series. It was different when the show was in first run and we welcomed any additional fixes between installments. The best part of Razor
isn't on the DVD anyway...the Quiznos commercial.
Stick with Season 4...you're getting there. I thought that the opening arc of the second half of the season was the best that they'd done since the Kobol and New Caprica arcs, but YMMV.