Firstly Welcome.
I'd say a search will pull up some comparisons of 34 gtt's vs 33gtr's as im sure a few people have asked the question,
That said, i believe that the general consensus will be that a gtr is a gtr, and that will out perform the 34gtt. The 34 on the other hand has a nicer newer interior.
If you are after performance you are probably best off going for the gtr, as long as you can afford maintenance costs as many people will tell you they can be costly if/when things start to go pear shaped.(rebuild?)
That aside, the 34gtt is a great car, comfy and quick. And a fair few manual examples around for sale at the moment for 18-23k, some more modded than others.
Good luck with the purchase