A brief glance at the datasheet suggests that the el86 is better with lower voltage, higher current and a lower Raa (primary impedance). Power is about the same so that's not an issue. You would need to know (or discern) the primary of the OT in question. And how much "higher voltage" are we talking about??? Further, a bigger resistor for the screen feed in the HV rail is "ok" but not ideal. You can quickly pigeon hole yourself into a very specific (and saggy) tonal character. This assumes you are building a guitar amp.