hey Fraser, welcome to the forum!
I recommend the 3x150 Halides, good choice for your tank size and depth.
Of course if you want to transition into marine you have a good point, the 250x3 would be a better fit for reefing. 250x3 would be a bit much for a planted tank, probably more difficult to keep stability. Are any of the fixtures you are looking at also with supplemental PC or T5 bulbs? If so, and you go with the 250x3, you could run supplemental bulbs part of the day and a shorter period of MH.
in the end, I still say go with the 150x3 - but I've moved on past reefing long ago. Too much $$$
