Ok, I'll start by apologizing if I am not seeing the picture here. I've been up all weekend with a sick 2 1/2yr old. Not much sleep to speak of.

"I've got 4 separate sub enclosures with terminal cups. Each cab is 8ohms and I was running two cabs wired in parallel for a 4 ohm load and running my sub amp in stereo. Now...how do I wire the 4subs in series to create a single 8ohm load"
I read this as 4 total subs at 4 ohms per side on 1 amp. LTD02 showed how to make this an 8 ohm load.

"I've got a total of four 2 ohm cabs and would like to bridge them all together for an 8ohm load. Two cabs are wired in series for 4ohms per side. How do I wire in series to the other 2 cabs to achieve 8ohms?"
I read this as 4 total subs at 4 ohms per side on 1 amp. LTD02 showed how to make this an 8 ohm load.

"Right now with 4 subs per side I'm at 95db efficiency. I'm gonna rewire to be 98db and run my amp bridged so an even easier load and more efficient."
I read this as 8 total subs at ? ohms per side on 1 amp.

"Now from those four wired in series to the next four achieves another 3db."
As it stands from the two examples provided by LTD02, if you wire these in series you will have a 16 ohm load. I might be missing something obvious, not sure my reading skills are up to par. Sorry if I'm confusing an issue that you already have worked out.