Stop measuring your swap space in terms of disk space, start imagining it in terms of "amount of time it takes to fill up". At a nice round 20MB/sec write, it would take a solid 400 seconds to use that much swap at full speed. In reality, you can't fill it that fast either, because it's seeking, also yanking other stuff out to run your other processes, and then sticking the stuff back in to run those other processes, so it's really a mess; the real amount of time it could take just to make initial real use of 8GB of swap could be
days, no joke. (In other words, I don't care if you have a 80MB/s drive, it really doesn't matter much, plus swap usage tends to be full of seeks anyhow so it's not like you're going to get 20MB/s either.) Given that a modern system is, relatively speaking, brought to a near-complete halt by being in swap, what possible process are you going to run where you are willing to put up with your system being brought to a halt for even tens of minutes at a time, let alone the hours or days it'll take to fully utilize 8GB?
Clearly, you don't need and basically can't use an 8GB swap partition. So, how long are you willing to put up with? That will vary, but let's say 10 seconds before you're "flipping out and killing processes". That's a 200MB swap partition. But... that's only 5% of the size of your RAM! If that's the difference between a process completing or not, you've probably already lost. Or you should just kill Firefox.
On a 4GB system, the most likely reason a process is pushing you into swap is that it is in an infinite allocation loop, and all having 4GB of swap does is make your system crawl that much more before the process dies.
This is a result of RAM sizes increasing far faster than hard drive write speed has. When I had 32MB of RAM, it made sense to have some swap. I could swap out, say, 16MB of unused executable pages (bits of windows, bits of drivers I'm not using, bits of the massive Office suite I'm not using, etc) and get that much more working set, and this could happen in a reasonable time; the system choked for a couple of seconds but recovered in a stable manner. Now swapping out 16MB of executable is a joke. SSDs may change the balance, but these balances have been out of whack for a long time, I rather suspect that even with an SSD it won't be worth swap. Especially since by the time SSDs are truly common 8GBs of RAM may be entry-level because, well, why not? (Poking at Best Buy really quickly, at the $500 line you get 4GB for laptops, a little over $300 for desktops, coming down fast. I'm not sure they have anything less than 2GB now and even that is really into "don't use swap" for the average user.)