Blackbird's due in a week and a half (provided Brandon doesn't decide to make his vacation permanent ;-) and have been researching tarps.

I'm getting old and crotchety and don't do much cold-weather camping, so rain coverage and weight are my priorities. Also, spouse is a bit sensitive about me having just spent $160 on a hammock, so I'm being cautious about the $$$. Here's where I am so far:

Pros: Well-made, light (10.2oz), roomy.
Cons: Expensive, hex requires extra more stakes than square

JRB 8x8
Pros: Fast and easy to pitch, light (9.4oz)
Cons: Moderately expensive, less coverage and room

Current Tarp
A 5x7 rain fly I picked up from REI or EMS some years ago. It provides adequate coverage for my ENO Singlenest (barely), but is probably too small to be useful for the incoming WBBB, true?
Pros: Free, seriously waterproof
Cons: Small (5x7), heavy (24oz)

Per the "Blackcat" instructions
Pros: Light, customized, inexpensive
Cons: My DIY skills are pretty much limited to cooking and making chocolate.

Thoughts? Recommendations? Other suggestions?
What size tarp should I be looking at for a WBBB?