I'm currently using a 12-34 cassette and a deore long cage derailleur on my mt bike set up. Has any run the new HG-61 SLX 9 speed cassette without the new shadow rear derailleur? The 2 tooth difference should be ok . I'm running a 1x9 drive train with a 32 tooth up front.
if you have a problem look at rotating the derailluer back by adjusting the B screw. On the SLX that I built for a friend this summer I had to get a longer screw to get enough clearance so the wheels on the SLX long cage did not make contact with the 34 cassette ring. With a 1X9 and the proper chain length you should have no problem.