Always go skinny on tires!! and Yes, yo u can do 65 on 30'', however, its not as fun as you might think. Depending on the type of tire you buy, Bias ply (which is what I previously had) or radial, there will be a difference on how much noise the tires make on the road since there aren't many options for that size tire and pattern. I usually drove 60mph with 30x7.0in tires on interstate but it actually did sound better at 55 mph. Still A 5MPH difference shouldn't be too noticeable. By the way, the fastest I tried driving my 40 on 30'' was 80mph for about a 20 second burst on those small doughnuts. It was smooth.
I upgraded to 32 inch bias-ply 16-tires. They are 7.5 inches wide. Just the 2 inches of rubber overdrive did make a difference. That, plus the tread on my tires were less aggressive; so there was a lot less road noise. It really depends on what you want out of your land cruiser. I wanted to give mine the "world market" look so i opted out for 16 in rims. the cruiser runs really really happy at 60mph. 65 isn't bad either. They are pricey tho, which is unfortunate. But its a decision i have not regret making.
Edit: The rims are pricey for 16in rims. I think a bit over double the price for standard 15 in toyota rims. The 15 tires cost me about $95 per rubber tire. The 16in tires cost me $120-135 per rubber tire from what I remember. What ever will make you happy driving your land cruiser. Good luck!!
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