E71T-1 has a faster freezing slag system than E70T-1 FCAW electrodes to accomodate out of position welds, so there is some increase in the chance for lack of fusion issues in horizontal fillets... That being said, those chances are about nill if you use high quality electrodes and have your process under control.

Parameter selection (within the ranges of your WPS) are more important with FCAW, and are directly linked to brand.  The flux/slag systems from each manufacturer are slightly different and that means that often the best operating parameters are slightly different..

I think you can prolly do just fine and eliminate any confusion by going with E71T-1 for all your production welds.

Both ESAB, Hobart, Lincoln and Corex make E71T-1 electrodes that can run .045 dia at 450 inches per minute out of position with mixed gas, and even faster in the flat and horizontal positions...  I'm not sure the deposition rates for the E70T-1's are that much better, and the limitations make it necessary to switch electrodes for out of position work.

In general terms, E71T-1M must be about the easiest and most forgiving electrode ever built.  It has great operator appeal.  It tends to operate over a wide wire speed range, and for a given wire speed the workable voltage and stickout is relatively broad. 

The slag comes off easy and the electrode is not prone to undercut.  Works great in all positions and on pipe.

It is not prone to internal discontinuities unless the welder is doing something substantially wrong.  The only common mistake I see low skilled guys prone to making with this wire is the same problem you see low skilled guys making with other wires - trying to hog in a fatty, and then experiencing slag inclusions or lack of fusion.

Only downsides I can come up with is it generates a lot of smoke, and for skilled welders it can get quite boring rather quickly.  Since it is so forgiving, it just isn't a very challenging electrode to weld.  That aside, if I am going to fabricate something from steel in the shop, I am going to use E71T-1M unless there is a good reason to be using something else.  It is just so fast and easy to produce good looking sound welds.  It gets the job done right and quick.

Personally I like ESAB 710X-M.  Made in Hanover, PA, USA.

BTW I would stick to the M for out of position work.  Some places go with E71T-1 and cheaper CO2 gas.  In my experience if you do a lot of vertical and especially overhead, you are ahead to pop for the -M and mixed gas so the welders spend their time welding and not digging spatter out of the their gun nozzles.