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If you are looking to save some money, subscribe to the lensrentals.com RSS feed. They've had the TS-E 45 and 90 up for sale recently. Actually, they still have one of each listed right now.
I have both. You'll get more of a miniaturization effect with the 45, but the 90 is better for near macro type work because of its close focusing ability, and you can use both with the extension tubes and teleconverters. The issue IMO with the 45 is quite strong CA, which is difficult to correct correctly if the lens has been shifted because the degree of CA is stronger in the corners closer to the edge of the image circle. Otherwise I think the 45 is decent, and despite the CA, tend to use it more than the 90. And the 90 has a nice quality and is sharp enough. That said, I use the 17 more than both.
Keep in mind the effect of the tilt function is stronger the wider the lens, and the farther away the subject is. Therefore, while the tilt of the 90 can be useful for near-macro work to keep focus along a plane not parallel to the sensor, the degree of tilt off parallel will not be as much as you might think at close distances.