They're (S13 and S14 KA-DE) both 9.5 compression. SOHC's had some different CR's.
All 91-94 S13's have the same cams.
S13 cams are 240/248 duration.
S14 cams are 232/232 duration.
Yes, putting S13 cams into an S14 KA will pick up power.
S14 KA's have lower redlines because there is no extra power (due to small cams) from reving it higher.
Yes, a dual 248 (that's dual exhaust cams) setup will breathe better in the higher rpms, but you need to watch your cam timing. It probably won't help, or possibly hurt low-mid power just based on general knowledge on what cam durations do.