A lot of these new bents are bred for putting greens; for extreme low mowing heights and tremendous amounts of leaves per square inch etc. They do have huge root systems, and I spoke with a superintendent who never watered his A-series greens in 2007, except to rinse in fertilizers and topdressing once per week. What I can't tell you is how they would perform at a half inch fairway cut. I would be concerned about managing the thatch that they might develop on such big acrerages as is common on fairways.
Penneagle was originally bred for greens in the early 1980's. As a putting turf it was too weak, but at fairway height it performs the best of any "manicured" fairway turf out there, and it does not thatch up on you. I have allowed Penneagle to go completely dormant for over a week and it came back, but the key with that management stratedgy is to keep the carts off it. Any bentgrass, when it it dormant, will be damaged by traffic.
The other issue here is soils. If you have tight clay soils and you let them compelety dry out, they are very difficult to re-wet. I feel that a certain amount of water needs to be applied in the interest of water conservation. The presence of somee water in tight soils, helps to draw additional water in, but when there is no water, there is a period of runoff and waste of water before there is penetration.
Rye grass is not a tillering plant. Rye grass plants are generally originated from seed, whereas blue and bent, and some fescue plants may originate from a mother plant that has sent a tiller out to colonize an area. Rye's drought tolerance mechanism is limited to the depth of the root system. In Illinois most of the great ryegrass fairways that were in the central and lower regions of the state were hit hard by grey leaf spot. The cost of spraying to keep out the leaf spot doesn't seem to make rye any less expensive than the cost of maintaining bentgrass, and there is no overwhelming difference in rye's water requirements verse bent.