I have been using PJ since 1992 (my 1st PJ was a $10K SharpVision DLP), but I'm no expert and probably less critical than some people when it comes to PJ. As long as the picture is bright and vibrant/beautiful, I am happy.
And if I were deciding on the 2 JVC PJ, I would go for 5500 since they are both pretty much the same overall to me in spec, especially the same lumens.
If the 7500 were 2,000 or 2,500 lumens, then I would go with the 7500. But since they both have the same brightness, I would go with the 5500.