I can't comment on specifics with the 5/64" NR233, but I have a bit of experience with .072" NR233 and alot of experience with the very similar NR232 and Coreshield 8.

NR 233 has a little bit softer arc than 232, it is more similar to Core 8.  You will likely find that with .072" a little more wire speed, say 170 or 175 IPM will help.  Likewise you may want to shorten the stickout a bit for the root.  Both of these changes will of course ramp up your amperage some.

A drag is good.  You may need a pretty aggressive drag on the root to hold the slag back, particularly for the first couple of inches when the base metal is dead cold.

As far as voltage goes, I don't know if you are giving load voltage or arc voltage, but in any case you need it low enough to allow good (reasonably close) slag follow and digging in the root, but high enough to prevent excessive convexity.  If you go too high you may see gas tracks, have the puddle spill out, see slag "islanding", have slag stick to the weld face, and lose penetration at the root.

I would try to keep the root pass reasonably thin.  You certainly don't want to outrun your slag, but if you put in an excessively thick root it becomes more likely that molten metal and slag will get between the arc and the base metal, increasing the likelyhood of inclusions / LOF.

BTW - I have written a fair bit about NR 232 in the forum here which is quite similar to 233.  If you search my user name and "232" you may find some info that may be helpful.

Good luck on your test!

Hello Paidslave, are you responsible for your own plate set-up? If so, be sure that you have the edges of each of the plates prepared to a knife-edge for starters, also be sure that you have carefully ground all of the mill scale back from the edge of the bevel on the surface of the plates where they fit against the backing strip. Be sure to remove all of the mill scale from the backing strip surface where it comes into contact against each edge of each plate. FLAT & TIGHT is how the edges of each plate should fit against the backing strip. Careful grinding is one of the key components to being able to put in a successful root pass that is free of slag inclusions, the mating surfaces should not have any gaps of any kind. You do want to use a slight drag angle going up on the vertical plate and possibly a bit more of a drag angle on the overhead one. If you do not have your backing down tight or if you have a land of some sort on the bevel edge of your plates this could promote trapping of slag. I am assuming that you are using a slight weaving progression as you are filling the root on each of these plates, try not to use any kind of a rapid motion or a whip of any sort, this could attribute to trapping slag along an edge or in the center. Slow and steady, or fluid if you will, should describe your progression. You mentioned that these plates are X-rayed, how wide is the backing strip? Generally the backing should be 3" minimum in width if they are X-rayed, the edges of narrower backing strips could possibly be seen as lines in the weld zone and misread as slag lines.
     You mentioned your welding parameters, they sound as though they are in the ball park, yet it is sometimes hard to say considering that you may or may not have a calibrated source and anyone elses comparison figures might be based on a calibrated or not calibrated system. It is likely that so long as you have a complete coverage of slag on the completed beads that you are close enough. If you see "bare" spots along the weld, then you might need to increase your wire speed slightly, if the wire appears to "stub out" you may need to decrease speed a bit. Good luck on the challenge ahead and best regards, Allan