It is generally thought that mixing manufacturers, and changing one tire without the other is less than ideal. Manufacturers design a front/rear combination to work together and get you the optimum grip, in the conditions the tires are designed for (track, street, touring, rain, etc). It really depends on how aggressive your riding style is. I personally replace a tire when it gets worn, and I mix manufacturers. I replaced my rear stock Dunlop at 8,000 miles with an Avon Roadrunner. I then replaced my front stock Dunlop at 13,000 miles with an Avon Roadrunner. I also ride with the knowledge that the front and the back tire aren't "matched", so I ride more carefully.
On the other hand, you're really messing with tire design by going up 20mm in rear tire size, which negates everything I've said above. Therefor, since you're changing your geometry anyway by going to the bigger rear tire, I don't think the other factors of matching front/rear is going to be as apparent as the much different handling characteristics of a 150 in the rear. So I would say, in your case, you don't need to worry about it...
Let us know how that 150 works out.