With those Kenwoods, I had the previous models when I first got into car audio and for entry level they were good at lower levels. They distorted pretty easy at higher levels and I only had about 300w to each of mine. But for the price installed in a Honda Integra I was impressed. I wouldn't pay more than 50 for them though. You can get the newer models on sonicelectronix for $60 with free shipping.
Well, I have personal experience with them and I have one on it's way back to parts express after one week of usage. Running a 12" HO -44 in .85 cuft net volume stuff with poly and pushing it at 700wrms with a ARC Audio XDi amp. Sounds great, gets loud, and comes apart nicely
Something in the voicecoil detached. I'm going to try the replacement when they send it back, but I'm not sure it's going to last either. I think the issue is at high volumes and low Freq when the VC is pulling the cone back down into the compressed small box it would be my assumption that the whatever adhesive they use on the cone attachement is failing. I did some testing that first week with some test tones and then ran through the popular 20-40 bass songs and it sounded great through it all, but I obviously killed it.
I've burned up some woofers in my time, but I can't say that I have ever mechanically damaged a woofer on less that rated power.