Hi JCase,
I have owned both Seawave and Solar as well as almost all Gumotex kayaks over the years. Right now, I only have a Solar and it seems to be the best all-arounder. I really like it.
You do lose a little bit of speed compared to Seawave, but it is more comfortable inside, especially as a tandem, turns better (better for rivers if you care for that sort of stuff-look at some pretty impressive youtube videos for that), has fewer D-rings, but enough and is almost half the price.
Seawave gets narrower as you move from the center and is overall more speed-oriented with v-bottom and all. That means when you go as tandem, it's really tight. It was even tight for my GF and she's in front (it was with the deck on though). Actually, Framura has more room inside, but you can go only solo on that one.
The deck on Seawave didn't work for me as my neanderthal legs are long and I like to move around. Better to invest in good pants/drysuit than decks. The I-beam in the middle of the floor was quite uncomfortable as it protrudes up and down, but it makes the boat much more rigid and you can really inflate it harder than other boats.
Don't get me wrong, Seawave is one badass boat and is probably the best that can be bought right now, in that category anyway. If I was paddling single most of the time, it would be my choice.
Solar keeps its width as it moves front and back form the middle of the boat. It has the same capacity though and is basically a stretched version of Sunny, so you won't have many problems I had with Sunny (bending in the middle in single and shipping in water in tandem configuration).
Check out some pics of my Solar here;
http://s1045.photobucket.com/user/bayar ... lar%20410cThey are running a sale now, and it makes sense to get two boats (shipping cost is only slightly more for two)
Post if you have more specific questions, but you can't go wrong with Gumotex.
Best