I dunno anything about those brands, but that is the general definition for underdampening. The springs would keep bouncing for a little bit after you hit a bump, rather than quickly coming to a stop. "Overdampened" happens when the shocks are to stiff for the springs: it'd take longer for your car to return to normal height after dipping or rising off a bump and you'd wear out the shocks real quick.

 

I ran a KYB GR-2 with Racing beat springs setup on my FB and plan on running a similar setup on my FC. Pretty cheap setup (about $450 for the setup) and I liked it. I believe you can get a set of tein springs on ebay for $184 if you are on a budget. You will get what you pay for regardless but any new suspension will be an upgrade from 21 year old parts.

 

I've heard that second to the RSR Racing springs are the Tanabe GF210s, which are linear. Would I have any underdampening problems with those?

 

On my FC I have B&G springs and Tokico HP shocks, I would not recommend getting the HPs. The ride quality of my setup is worse than what I'd like and the shocks are underdamped, it's not bouncing all over the place but on road sections that dip up and down there is excessive vertical motion. I like the springs but the tokicos get a thumbs down from me. I had illuminas on a previous car and they were up to the task of linear springs and a big drop but the ride wasn't the best either. It really depends on what you're using the car for if it's going to be a daily driver you'd be nuts not to get progressive springs

 

search but this is what im running, look in my signature.