So, I've been gradually building an ever more elaborate Oblivion-with-mods install and there's not much left to do aside from picking a suitable combat system enhancer.
I've heard good things about both Deadly reflex and Unnecessary violence and wanted to get the community's opinion on which to pick.
I'd also like to know if anyone has encountered game breaking errors with either mod, considering I'd be using FCOM and such things as Supreme Magicka and Duke Patrick's Archery to boot.
Any input would be much appreciated.

You might want to give http://www.gamesas.com/index.php?/topic/1215917-duke-patricks-melee-combat-no-recoil a shot, I've never used it myself but it looks pretty good. I gave a try to Deadly Reflex but I really don't like it as it basically transforms Oblivion to Ninja Gaiden

If you already use (and like?) Duke Patrick's Combat Archery, why not also use his "Melee Combat NO RECOIL"?

Similar in nature, and worth a try, I think,

Otherwise, try either of those other mods, and see what suits your purposes. I have heard that the latest version of Deadly Reflex is very buggy, and therefore, the previous version might be a safer bet, as it were. The new version of Unnecessary Violence has not been released yet, as far as I am aware, and in fact, it could be that the modder in question will not be completing it...? You would of course need to investigate that for yourself. I am not that familiar with either of these mods, as their style does not greatly appeal.