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Now you can see how the wheel spacers will give you the extra tire clearance at the perch. I want to say with the 2" spacers on mine it puts the edge of the tire somewhere right at the outside edge of the perch. I could have fit larger tires but went smaller and should probably go to smaller spacers like 1" to 1.5" to fix the edge of my tire hitting the top of the fender when bottoming out.

Yeah, the very inside of the back tires will rub pretty easily on the spring perch if you're not careful with your tire size, especially with a more square tire tread. looks like your current tires are pretty rounded on the inside... the fronts can fit whatever pretty easily.

The rx400h has rear struts, the 450h has the spring and shocks

I think you're stuck with 235/65r17's as your biggest, I had the next gen 235/55r19's and they would sometimes rub going around corners. I can only fit 265/70r17 cause I put 2012 highlander rear struts in it. That leaves you just over 29".

The world of lifting RX vehicles is still pretty small so there aren't exactly any definitive guides but like any other strutted vehicle the same limitations in tire/wheel fitment would apply. The first limitation on my 300 was the rear spring perches because they are squattier than the fronts. Side clearance of the spring perch will limit how tall and wide of a tire you can fit without modification or for a certain offset/spacer. The next limitation for me was rubbing when turned full clock, not acceptable to me and I was able to fit mine with no rubbing. The taller and wider the tire the turning clearance is greatly reduced, its geometry but you can figure it out with a straight edge. Clock the wheels and take a straight edge across the inside sidewalls to the nearest obstruction and you can measure how much taller of a tire will fit without rubbing but leave some cushion. The closest point of the tire should be at the horizontal axis of the tire but make sure you look at fender clearances as well. Just take your time and measure everything until you are absolutely sure your fitment is what you want. You could also likely take it to a custom shop and they should be able to measure or use a jig to tell you what you can and can't fit. I would not recommend bringing the tire tread up past the bottom of the spring perch. If you do and you do not have ample clearances you can easily slash your sidewalls. If you are sticking with stock suspension the steering changes shouldn't be as drastic but just be ready for it to handle differently. I have not had to trim anything for mine and do not have anything rub except when I have 300-400 extra pounds in it and the suspension takes a really hard hit, mostly the rear where the outside tread just catches the lip of the fender. I need a little more travel or slightly stiffer springs in the rear. I think I am also running a larger wheel spacer than necessary (2"). Same thing for the front but don't hit the fender lip unless it is a really really hard suspension hit and I am turning. There is enough travel and clearance in the front if I am going straight over that really hard hit. I do not rub on the inside of the tire when turning but it is the outside front of the tire that hits the fender liner. That is only because it was a cheap aftermarket liner I was in a hurry to get in there to get some protection for my trans cooler before a trip. I had to cut the vents into the plastic and they puckered out into the wheel well so the tire catches them. I need to reinstall it so it fits correctly and likely make a little aluminum plate/grill for the vent slots so that doesn't happen. ***Edit- Brickwall says you have springs and shocks on the rear of yours and not a strut so that makes it a lot easier. You are then pretty much limited by the strut and turning clearance of the front then,

Air is 80% Nitrogen.