worth the jump to Cornwall IV's from Forte IV's?

Check your measurements again. The La Scala about the same width as a CW and  is only 10" deeper. It can also sit flush against the wall.

And as @ozzy62 pointed out, the sound is something to behold, subs or not (as in my case). My advice is to not sneak up on what you want; just plan and go for it. It will cost less in the end.

Keep the Fortes. An upgrade would be Volti. 

I have replaced Cornwalls with Audio Kinesis "Jazz Module" (you can see that speaker on YouTube in my system composed of Atma Sphere amplification and TEAC vrds CD player). That particular model is not in production right now but shall be available again in october. Few other models from AudioKinesis will do a better job than Cornwalls (namely Azel and Gina with subs) particularly in the rendition of the stage / space. More importantly, you can contact Duke (the guy behind Audio Kinesis) and discuss with him about your needs. A better amplifier may be something to look into, as sometimes good speakers like Forte's are underexploited by poor amplification. La Scalla and Volti are very fine, but too big for any room and, let's be honest, ugly. 

Volti Razz speakers are about the same size as the Forte IV so I dont know what the "dolphin" guy is talking about.. Lascalas weigh twice as much as the Cornwallls (200 pounds) so keep that in mind if you live alone. Floor space isnt the only consideration. Forte are a pain in the ass to set up properly and are the least forgiving speaker in the Heritage lineup. Poor recordings (like ROCK) will make themselves known. If you can afford the Volti’s its a definite step up from the Klipsch. Better parts, crossovers/wiring etc and you dont have to do any work to them to make them sound great. All Klipsch speakers need Dynamat placed inside the cabinet to yield the best results. Ive had ALL of the Speakers mentioned above except the La Scala’s and Heresy.

Check out Andrew Robinson's channel on Youtube on this very topic: