That's too low. You can get 1200 H/s from your card -> http://www.whattomine.com/
Default(start) values are adapted for 1000 kh/s of Scrypt(280x). (copyed from whattomine)
A 750ti does roughly 260Khs scrypt can be bumped to about 330Khs with oc and the bios mod for more power. 1,2Khs was maybe true when nf was 15 but not at nf 16. If you know a config for a 750ti that does 1,2Khs at nf 16 then by all means please post it.
1000 H/s for a 280x and 1200 H/s for a 750ti, those are the default values for Chacha Nf16. Are you saying that both are too high?
It calculates it after the scrypt hash rate, the default rate they put in is 1000Khs. Try changing the scrypt hash rate and see what happens in the chacha hash rate tab. My r9 280x runs 760Khs in scrypt mode but only 255Hs when mining YAC, my 750ti run 336Khs in scrypt mode and 240Hs mining YAC, both speeds are at current N factor 16. Basicaly its just gives you a rough estimate of hash rate for the diffrent algo when you put in the scrypt hash rate.
Could you please tell us the power usage on your cards to get those 255 H/s (R9 280x) and 240 H/s(750Ti)? Thank you!
Tbh i have no idea as i dont have the gear to measure it on my test setup, i know the 750ti is TDP locked @ 38,5watts i have 2 of thees just for testing purpose. One of them is flashed to 65,5watts TDP while the other one is stock TDP. Crypto mining blog already did some testing on 750ti http://cryptomining-blog.com/tag/gtx-750-ti-power-consumption/ http://cryptomining-blog.com/3036-power-usage-of-geforce-gtx-750-ti-with-various-crypto-algorithms/
The r9 280x https://litecoin.info/Mining_hardware_comparison or simply google r9 280x dc2t 3gd5 mining power consumption there will be plenty of reading on people oc and undervolting thoes cards.
Hope that helped abit